 When the Scottish National Party (SNP) withdrew support for the Scotland Act 1978, a vote of no confidence was held and passed by one vote on 28 March 1979, forcing Callaghan to call a general election.As the previous election had been held in October 1974, Labour could have held on until the autumn of 1979 if it had not been for the lost confidence vote.Margaret Thatcher had won her party's 1975 leadership election over former leader Edward Heath.