Support for the SNP reached 30% in the October 1974 general election, with 11 SNP MPs being elected. In 1978 the Labour government passed the Scotland Act which legislated for the establishment of a Scottish Assembly, provided the Scots voted for such in a referendum. However, the Labour Party was bitterly divided on the subject of devolution. An amendment to the Scotland Act that had been proposed by Labour MP George Cunningham, who shortly afterwards defected to the newly formed Social Democratic Party (SDP), required 40% of the total electorate to vote in favour of an assembly. Despite officially favouring it, considerable numbers of Labour members opposed the establishment of an assembly. This division contributed to only a narrow 'Yes' majority being obtained, and the failure to reach Cunningham's 40% threshold. The 18 years of Conservative government, under Margaret Thatcher and then John Major, saw strong resistance to any proposal for devolution for Scotland, and for Wales.