The second half of the twentieth century saw two periods of Conservative ascendancy. The first was between 1951 and 1964, the second after 1979. Between 1964 and 1979 Britain returned to a more genuinely two-party system, with alternating governments. After narrowly winning the 1964 general election, Harold Wilson substantially increased his majority in 1966, only to lose to the Conservatives under Edward Heath in 1970. The election of February 1974 was indecisive. As leader of the party with the largest number of seats, however, Wilson returned to Downing Street and secured a working majority in a second general election in October. In 1976 Wilson retired in favour of Callaghan, who eventually lost the 1979 election to the new Conservative leader, Margaret Thatcher.
These fifteen years saw three developments which seemed at the time to override everything else, an impression which has not since been contradicted. First, it was a period of reform; various commissions recommended sweeping changes, and the political, social and economic sectors were all affected by a stream of legislation. Second, Britain was perpetually on a knife-edge, threatened by crisis after crisis. Governments were constantly challenged by balance of payments deficits, inflation, industrial disruption or political instability. And third, the post-war consensus that had been the basis of Labour and Conservative policies between 1945 and 1964 began to wear thin as both parties tried to find more distinctive solutions of their own. The failure of such attempts forced them back onto the middle ground but prepared the way for the real break, which came after the 1979 general election, one of the most decisive of the twentieth century.