On 29 January 2013, the government was defeated in the House of Commons on its policy to redraw constituency boundaries and reduce the size of the commons chamber. MPs voted by 334 to 292 to accept an amendment agreed by peers, meaning the planned boundary reforms were postponed until after the general election scheduled for 2015.

The defeat was orchestrated by the Liberal Democrats, the Conservative Party’s junior coalition partner, who voted with the Labour opposition against their own government’s legislation. Four Conservative MPs – David Davis, Philip Davies, Richard Shepherd and John Baron – also rebelled.

It marked the first time that Liberal Democrat ministers in the commons, including deputy prime minister Nick Clegg, voted against the Conservatives on a piece of coalition legislation.

The division reflected a complete split between Conservative and Liberal Democrat ministers.

The move was styled as an act of retaliation after Conservative backbenchers blocked the coalition’s proposals, spearheaded by the Liberal Democrats, to reform the House of Lords the previous year.

On 10 July 2012, 91 Conservative backbenchers rebelled against the House of Lords Reform Bill – the largest rebellion of the 2010-2015 parliament. At the time, it also marked the largest rebellion by government MPs on the second reading of any bill since the Second World War.

The House of Lords Reform Bill would have provided for an upper chamber of 450 members (halved from 826), 80% of whom would be elected – with the reforms to be completed by 2025. The remaining 20% of non-elected members (90) would be appointed by a statutory appointments commission on a non-party basis.

One-third of the elected members would have been chosen at the 2015 general election, another third at future elections set for 2020 and 2025 – 120 members in each election. Under the proposals, existing peers would be “phased” out as elected members were brought in.

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At the outset of the debate on 10 July 2012, the leader of the House, Sir George Young, announced the government would withdraw the bill’s “programme motion” – the timetable designed to limit debate. Labour MPs were set to join forces with the Conservative rebels to reject the motion, ostensibly on the grounds it would not provide adequate opportunity for scrutiny.

Young stated: “We have listened carefully to the debate so far, confident that we will get a significant majority on second reading tonight. But for Lords reform to progress, it needs those who support reform to vote for reform and to vote for that reform to make progress through this House.

“It is clear that the opposition are not prepared to do that, so we will not move the programme motion tonight.”

Speaking in favour of the bill, Young said there was nothing Conservative about “retaining a wholly appointed upper House in the 21st century”.

Conservative MP Christopher Pincher suggested that giving the Lords power without final responsibility was “a bit like what [former prime minister] Stanley Baldwin described as the prerogative of the harlot throughout the ages.”

Conservative MP Conor Burns resigned as a parliamentary private secretary (PPS) over the proposals. “I shall leave this chamber with my head held high, able to look myself in the mirror”, he told the House.

Burns added: “The House of Lords works. It has stood the test of time. We abolish it at our peril.”

The rebel ringleader, Conservative MP Jesse Norman, dismissed the bill. He called it an “interesting solution to an elective dictatorship to propose two elective dictatorships.”

During the division that followed, the prime minister, David Cameron, personally confronted Norman in the members’ lobby. In his 2019 memoir, For the Record, Cameron alleged that Norman had sent a message to Tory MPs giving the impression that he, as prime minister, now wanted the bill defeated.

Norman reportedly texted: “The PM desperately needs the bill to be knocked off. There is no manifesto commitment now that the programme motion has been withdrawn.”

Cameron recalled confronting Norman, admitting that his “even temper left me right there.”

The House of Lords Reform Bill received its second reading by 462 votes to 124 – but the lack of an agreed timetable cast significant doubt on the government’s ability to carry it through parliament. Without a programme motion, the bill could – and surely would – have been subjected to fatal filibustering.

The Conservative rebellion also featured 19 abstentions. Tory MP Angie Bray was dismissed as a PPS after voting against the bill.

Shortly after the vote, Norman described the proposed legislation as “a dead duck”.

In a statement on 6 August 2012, Nick Clegg confirmed the government would withdraw the bill, accusing the Conservatives of “breaking” the coalition contract.

Clegg stated: “My party has held to that contract even when it meant voting for things that we found difficult. The Liberal Democrats are proving ourselves to be a mature and competent party of Government and I am proud that we have met our obligations.

“But the Conservative party is not honouring the commitment to Lords reform and, as a result, part of our contract has now been broken.

“Clearly I cannot permit a situation where Conservative rebels can pick and choose the parts of the contract they like, while Liberal Democrat MPs are bound to the entire agreement.”

He announced that the Liberal Democrats would retaliate by instructing its MPs to oppose the Conservative-driven boundary changes.

Clegg revealed that he had told Cameron, his coalition partner, that when “parliament votes on boundary changes for the 2015 election I will be instructing my party to oppose them.”

The deputy prime minister argued that this approach would “restore balance to the coalition agreement.”

In his press conference, Clegg also criticised Labour for their approach to Lords reform, saying they were “supporting the ends, but – when push comes to shove – obstructing the means”.

The House of Lords Reform Bill was formally withdrawn on 3 September 2012, when Clegg made a commons “statement on House of Lords reform – or what is left of it”.

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On 29 January 2013, the commons considered a House of Lords amendment to the Electoral Registration and Administration Bill to postpone the boundary review until 2018.

The Conservative leader of the House, Andrew Lansley, clarified that he was not setting out “formally the view of the government, as there is not a settled coalition view” – accounting for the Liberal Democrat position. He confirmed that collective ministerial responsibility had “been set aside for this debate.”

Lansley proceeded to mount a robust defence of the boundary reform proposals.

He stated: “In England, East Ham has 92,000 voters; Wirral West has just 55,000. The differences are even greater in respect of other nations; Arfon in Wales has an electorate of just 41,000.

“This means that some votes count much more than others, and the principle of greater equality in the value of each vote is at the heart of this new boundary review.”

Lansley argued that reducing the number of MPs by 50 would save the taxpayer £13.5 million a year.

John Thurso, a backbench Liberal Democrat MP, made the case for delay. He argued that the coalition agreement was a “slate” rather than a “pick-and-mix menu.”

Thurso stated that because the Conservatives had blocked Lords reform, he could no longer “in all conscience” support the boundaries policy.

Thurso also addressed the irony that the rebellion on boundary reform would come in a vote on a Lords amendment.

He told the House: “I gently point out to my friends on the government benches, in the mildest manner possible, that they have got what they wanted: the great, the good, the wise, the academic, the apolitical, the ex-public servants and the generals, whom they strove so hard to protect, have come together in their wisdom and given us amendment 5.

“I beg the House to support it.”

Conservative MP Penny Mordaunt accused the Liberal Democrats of “spite, pettiness and self-interest.” She accused the party of making “flirtatious glances” toward Labour as potential coalition partners ahead of the 2015 general election.

Mordaunt stated: “The Liberals have exchanged their legendary sandals for flip-flops in the hope that that will enable them to keep their options open, but they would be wrong to think that the real damage they will do today is to the prospects of the Conservative victory in 2015 or to the notion of a Conservative government.”

Tory backbencher Peter Bone said that those Liberal Democrat ministers who voted against the government should resign.

He said: “The only honourable thing the Liberal Democrats can do tonight if they do not vote with Conservative members is resign from the government and cross the floor of the House.

“If they have any principle, any honesty, that is what they must do.”

Lords amendment 5 was ultimately agreed by 334 votes to 292 – a majority of 42.

The result ensured the 2015 general election would be fought on the existing 10-year-old electoral map.

Polling experts calculated that the defeat damaged Cameron’s chances of winning an overall majority in 2015. At the time, YouGov estimated that under existing boundaries, the Conservatives required an 11.1% lead to win a majority on a uniform swing, compared to the 7% lead required under the proposed revisions.

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MPs debated the principle of collective ministerial responsibility in Westminster Hall on 13 February 2013 – in light of the Liberal Democrat rebellion.

Conservative backbencher Christopher Chope argued that the situation of ministers answering in the commons “on behalf of not the government, but the Conservative party… was rather bizarre.”

He questioned why collective responsibility was set aside for the boundary review and delivered a sharp critique of the Liberal Democrats.

Chope said: “The Liberal Democrats have a history of speaking with forked tongue. They often enunciate a different policy for different groups of potential electors in different parts of the country…

“It seems as though their attitude towards speaking with forked tongue is tainting the whole government.”

Sir Nick Harvey, a former Liberal Democrat minister, defended the dynamics of the coalition.

He stated: “Collective responsibility, in the sense in which we have understood it, can exist only where there is a collective view, a collective agreement and a collective decision between the two parts of the coalition that they will proceed in a certain way.

“Where something breaks down… it is inevitable that we will not be able to apply a traditional doctrine.”

He added: “We should not fret about that or worry ourselves unduly about it.”

It fell to Chloe Smith, the parliamentary secretary for the Cabinet Office, to explain the government’s application of the collective ministerial responsibility doctrine.

Smith noted that the principle of collective responsibility began with George III as a way for the cabinet to prevent the king from playing ministers off against one another.

She told the chamber: “Collective ministerial responsibility is about how ministers behave towards the public and parliament, rather than towards the crown.

“However, the basic point remains the same: ministers need to be able to have frank discussions and disagreements in private, while maintaining a common purpose once a decision has been taken.”

Smith insisted that there was precedent for the adoption of an “agreement to differ” on contentious issues, pointing to the experience of the National Government in 1931.

She concluded by citing former Labour prime minister James Callaghan: “I certainly think that the doctrine should apply, except in cases where I announce that it does not.”

Smith maintained: “That demonstrates that the terms, duration and enforcement of the arrangement are ultimately a matter for the prime minister.

“It is most important to add that the current government have decided to set collective responsibility aside on some specific occasions. That is a fact of life in a coalition, and it shows how our constitutional practice can evolve to suit new situations.”

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The saga ultimately served as the catalyst for a “reboot” of the coalition.

In an attempt to recapture the spirit of the 2010 Rose Garden love-in, Cameron and Clegg conducted a joint press conference in January 2013. They insisted that the coalition would last a parliamentary term, giving Britain “strong, stable and determined leadership”.

Cameron and Clegg both described the coalition as a “Ronseal deal” which “does what it says on the tin”.

The conference coincided with the publication of a 46-page review of the coalition’s performance.

This period in the coalition’s lifespan was treated at some length in Cameron’s 2019 memoir. The former prime minister conceded that subjecting the boundary reform proposals to a vote was a “foolish mistake” that meant Clegg had the Conservatives in the “short hairs”.

He wrote: “We hadn’t ensured that boundary reform would go through automatically…

“Therefore the Lib Dems, combined with Labour, could make the passage of boundary reform dependent on Lords reform. They could make a false tit-for-tat link between Lords and boundaries. Which is exactly what they did.”

Cameron nonetheless said he felt “cheated” by Clegg over his approach.

He wrote: “I felt cheated by him. Here was this reasonable, decent person I had worked with for over two years being disingenuous and – frankly – dishonourable.”

Cameron also criticised those Conservative MPs who spoke in opposition to House of Lords reform, singling out supposed “modernisers” Norman, Mordaunt and Charlotte Leslie.

He wrote: “Some who, as far as I was aware, had never expressed a view on the Lords were now speaking about it like it was some great moral crusade… Were people really that passionate about keeping the Lords as they were? Or were they just anti-change, anti-coalition, or anti-me?”

He characterised the Conservative rebellion in the Lords as a “head-body problem” that highlighted the lack of ownership Tory MPs felt over the coalition agreement.

Cameron described a private drink with Clegg in January 2013 as representing a “renewal of our vows.”

He wrote: “The experience left us more hard-bitten, but we still wanted to make the coalition work. So these issues that brought us to the brink of divorce ended up in a renewal of our vows.”

At the time of the “mid-term review” – which came some weeks before the commons debate on constituency boundaries – Cameron recalled discussions over the prospect of a joint Conservative-Liberal Democrat ticket at the 2015 general election.

The ex-prime minister said that such plans were never considered “in any great detail”, however.