On 12 January 1971, two bombs exploded outside the north London home of Robert Carr, the secretary of state for employment.

Carr, a senior minister in Edward Heath’s Conservative government, was at home with his family at the time but was unhurt. The first device went off soon after 10:00 pm; the second detonated a few minutes later. Two days after the explosions, an anonymous letter was sent to newspapers by a group calling themselves the Angry Brigade, a small, far-left anarchist group.

The Angry Brigade was accused of carrying out 25 attacks on government buildings, embassies, corporations and the homes of Ministers between 1967 and 1971.

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The January 1971 bombing was a protest against the government’s Industrial Relations Bill, which Carr was responsible for steering through parliament. The proposed legislation, which aimed to curb the power of trade unions by introducing measures such as compulsory strike ballots and a new industrial court, had provoked widespread opposition from the labour movement.

The bill received its second reading in the House of Commons on 15 December 1970 by 324 votes to 280.

Describing what had happened, Carr said: “I had just opened my dispatch box to do my evening’s work and there was this loud explosion.

“The windows in the room we were in weren’t blown in, but it was obvious we could hear other windows blown in and when we looked out into the hall, the front door had been blown open.”

He added: “I think it would be wrong to associate this with anything at the moment. The police are investigating and until they’ve investigated it would really be very foolish and wrong to suggest anything at all.”

Harold Wilson, Labour leader of the opposition, said the use of violence “must be treated as a major crime.”

On 13 January, the home secretary, Reginald Maudling, told the commons that the police were hastily making “widespread inquiries” as to the nature of the bombing. The bomb, Maudling said, was of a “lethal character”.

He confirmed that “arrangements made for the protection of members of the Government are being urgently reviewed.”

The home secretary added: “I am confident that every member of the House would wish to join in unreserved condemnation of this crime.

“I am also sure that I would be reflecting the feeling of the House as a whole in expressing our sympathy with my right honourable friend and his family in this most unpleasant experience and our relief that they were physically unharmed.”

James Callaghan, the shadow home secretary, expressed his “profound hope that those who have committed this outrage will be brought to justice at the earliest possible moment”.

Jeremy Thorpe, the leader of the Liberal Party, said: “Surely the lesson to be learned by everyone is that the opportunity for persuasion lies not in the bomb but in the ballot box”.

On 18 January, Carr returned to the commons for the Industrial Relations Bill’s committee stage.

Barbara Castle, the shadow employment spokesperson, began by expressing how glad she was that Carr was “fit to be with us this afternoon”.

Castle added: “We congratulate him on surviving two physical hazards, though I am afraid we cannot guarantee that he will survive a third political hazard that lies ahead of him, namely, the passage of this bill. Indeed, we shall do our best to ensure that he does not.

“But our weapon will not be force; it will be argument. We hope that the government will not use force against us by trying to railroad this bill through without proper discussion.”

Carr told the commons: “I should like first to say to [Castle] a personal ‘Thank you’ for her kind remarks about me at the beginning of her speech.

“I wish to say to the House how much not only I myself but all my family appreciated the many messages we have had from very large numbers of honourable members on all sides of the House in view of our little, shall I say, ‘accident’ last week.”

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On 6 December 1972, a 111-day criminal trial – the longest criminal trial in British legal history – ended with two men and two women being jailed for 10 years for conspiring to cause explosions.

Carr went on to serve as home secretary (July 1972 to March 1974) and chancellor of the exchequer (March 1974 to February 1975). He co-founded the Tory Reform Group of moderate Conservatives in 1975.

He was viewed as a possible successor to Edward Heath as Conservative leader.

In the event, Carr served as interim or acting leader of the Conservative Party after Heath’s resignation as leader in 1975. It came after Heath was defeated in the first ballot of the 1975 Conservative leadership contest.

Margaret Thatcher, the winner of the 1975 Conservative leadership contest, did not appoint Carr to her shadow cabinet.

Carr was considered to be a close ally of Heath during his tenure as Tory leader and prime minister. He backed Heath’s candidacy in the 1975 contest.

In 1976, Carr was created a life peer as Baron Carr of Hadley.

In February 2002, a member of the Angry Brigade group issued a public apology to Carr. Reporting at the time revealed that the member in question, Jake Prescott, had also sent the Carr family a Christmas card.

Lady Carr said: “I still remember a Christmas card Jake Prescott sent us and it was the best Christmas present I ever had.”