At the time the rules for electing a party leader only applied when the post was vacant and there was no way to challenge an incumbent. Heath faced many critics calling for either his resignation or a change in the rules for leadership elections to allow for a challenge. Heath eventually agreed with the 1922 Committee that there would be a review of the rules for leadership elections and subsequently he would put himself up for re-election.
A review was conducted under the auspices of Heath's predecessor Sir Alec Douglas-Home. Two recommendations were made, though neither was to make a difference in 1975 (although they would prove crucial in future years). The leader would henceforth be elected annually, whether the party was in opposition or government, in the period following a Queen's Speech, though in most years this would prove a formality. Also on the first round the requirement for a victorious candidate to have a lead of 15% over their nearest rival was modified so that this would now be 15% of the total number of MPs, not just those voting for candidates.
Following the review, Heath called a leadership election for 4 February 1975, in order to assert his authority as leader of the party. Many expected the contest to be a walkover, believing there was no clear alternative to Heath after Keith Joseph had ruled himself out following controversial remarks calling on poor people to have less children and William Whitelaw had pledged loyalty to Heath. Many other shadow cabinet members pledged their support for Heath including Jim Prior, Peter Carrington, Leader in the House of Lords, and Robert Carr, Shadow Chancellor.
However Margaret Thatcher opted to stand, with Airey Neave as her campaign manager, as did backbencher Hugh Fraser. Even then many believed that Heath would win easily. Thatcher's support was seen as minimal, with all the Conservative daily newspapers backing Heath (although the weekly The Spectator backed Thatcher). As the election went on it became clear that the race was going to be much closer, as Thatcher became the clear candidate to be supported by discontented backbenchers. She also had the good luck of being able to attack the Labour government's finance bill in the Commons during the campaign, which showed off her credentials well despite the extra workload.
49-year-old Thatcher was the first (and to date the only) woman to be elected leader of a major political party in the United Kingdom. Whilst Margaret Beckett was interim leader of the Labour Party after John Smith's death in May 1994 until the election of Tony Blair in July 1994, and Harriet Harman served as acting Labour leader following Gordon Brown's resignation in May 2010 until September 2010, neither Beckett nor Harman was elected to such a position. Thatcher would also go on to become the nation's first female prime minister.