On 4 June 2009, the work and pensions secretary, James Purnell, resigned from the cabinet and called for the prime minister, Gordon Brown, to step down. The bombshell resignation came just minutes after the polls had closed in the European and local elections, in which Labour was forecast to suffer damaging defeats.

Purnell’s resignation followed a period of turmoil for the Brown government, which was dealing with the fallout of the MPs’ expenses scandal and suffering in the polls. The home secretary, Jacqui Smith, and the communities secretary, Hazel Blears, had announced their departures in the preceding days.

Both Blears and Smith were under fire over their expenses claims. But Blears did not pay the customary tribute to the prime minister; rather, the media spotted she was sporting a brooch with the message “rocking the boat” on the day of her resignation.

Purnell’s broadside marked the first and only direct challenge to Brown from a cabinet minister.

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In his resignation letter, which he also sent to the Times and Sun newspapers, Purnell stated that Brown’s continued leadership made a Conservative victory at the next general election “more, not less, likely”.

Purnell, a prominent Blairite, effectively described the prime minister as unelectable. He urged Brown to “stand aside to give our party a fighting chance of winning”.

Purnell wrote: “I now believe your continued leadership makes a Conservative victory more, not less likely. That would be disastrous for our country. This moment calls for stronger regulation, an active state, better public services, an open democracy.

“It calls for a government that measures itself by how it treats the poorest in society. Those are our values, not [Conservative leader] David Cameron’s.”

A spokesperson for Purnell said: “He feels Gordon should now stand aside to give the party a fighting chance of winning the next election. He is not seeking the leadership nor acting with anyone else. This is not about jobs or careers.”

According to a contemporary Guardian report, the source added: “He [Purnell] has made the decision in the last few weeks – he’s always been very loyal, but he now feels he can no longer go out and defend the prime minister. That is why he has taken the difficult decision to resign.”

A Downing Street spokesman responded: “The prime minister is disappointed by the resignation of James Purnell, of which he was informed shortly before 10:00 pm.”

In the 2009 European elections, Labour placed third with just 16% of the vote – behind the Conservative Party and the UK Independence Party (Ukip).

The resignation also came amid reports of a clandestine backbench revolt which planned to oust Brown. It was reported that a “go now” letter was being circulated in the Labour parliamentary party. Two senior backbenchers, Barry Sheerman and Graham Allen, followed Purnell in calling on Brown to step down.

Sheerman, the chair of the education select committee, told the BBC: “This goes far beyond just a few people, this is a large number of us who are really unhappy about the present situation.”

Allen, a former whip, hoped Brown would “take the honourable way out so the party can progress with a leadership election”.

David Miliband, the foreign secretary, and Alan Johnson, the health secretary, were both considered as possible successors had Brown been toppled. But they both rowed in behind the Downing Street incumbent. Purnell was also seen as a potential future leadership candidate – though he insisted he would not seek Brown’s post were it to become vacant.

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In response, Cameron denounced the “appalling, shambolic” state of the government and called for an immediate election.

The Conservative leader declared: “In a deep recession and political crisis we need a strong government. Instead we have a government falling apart in front of our eyes. Britain deserves better than this.

“With this resignation the argument for a general election has gone from being strong and powerful to completely unanswerable.

“For the sake of the country Gordon Brown must take the one final act of authority left open to him, go to the palace today and call the general election we have been demanding.”

In January 2010, two former cabinet ministers, Patricia Hewitt and Geoff Hoon, called for a secret ballot vote to resolve Brown’s future. The prime minister dismissed the challenge as a “form of silliness”, adding: “I am the prime minister and am determined to remain so. I am determined, I am resolute.”

Both Johnson and Miliband (eventually) signalled their support for the prime minister.

Purnell stood down as an MP at the 2010 general election.

Brown led Labour into the 2010 election, which resulted in a hung parliament.

Cameron’s Conservative Party won 306 seats with 36.1% of the vote, a net gain of 96 MPs compared to the notional 2005 result. Labour lost 91 seats, returning 258 MPs on a 29.0% vote share.

Brown resigned as prime minister on the evening of 11 May. Cameron entered 10 Downing Street at the head of a Conservative-Liberal Democrat coalition.