In retrospect Labour may have lost this election before the 1970 campaign began.
Economic crises had dogged the government, forcing the devaluation of sterling in 1967, industrial relations were consistently poor and the government upset many of its own supporters by backing the American war in Vietnam.
Prime Minster Harold Wilson was humiliated by the UK's rejected application for membership of the European Economic Community and the unpopularity of the government was shown in a record number of by-election defeats during the parliament - totalling 15.
Labour's attempt at trade union reform, Barbara Castle's In Place of Strife plan, also failed.
But by 1969 a turn round in the economy also saw a rise in Labour's fortunes and the polls soon began forecasting that the government could get another chance.
As it turned out the Conservatives were underestimated by observers. They had effectively re-jigged the party machine and had a strong and well organised grassroots network in place.
And according to some insiders Labour's HQ was in fact wrong footed by Wilson's decision to go to the polls in the summer.
The Liberals' campaign suffered somewhat as they struggled to break in a new leader, as Jo Grimond had been succeeded by Jeremy Thorpe.