Having just scraped home in 1964, Harold Wilson knew he would have to face the country again soon.
Labour's priority then must have been to project an image of a party fit to govern. But when the largest balance of payments deficit since the war was revealed it only highlighted the government's shaky position, as did defeat in the Leyton by-election.
The loss cut Labour's wafer thin majority and dashed the hopes of a Commons return for Wilson's choice of foreign secretary, Patrick Gordon-Walker.
But as 1965 saw Labour fare badly in local elections the Conservatives treated defeated leader Sir Alec Douglas Home with traditional ruthlessness, installing Edward Heath in his place.
In Heath the Tories hoped they had found their answer to Wilson. Oxford educated, the former Tory chief whip triumphed in a three-way contest, beating Reginald Maudling and Enoch Powell.
The tricky tactical position of the Liberals was made plain when Labour ignored overtures from party leader Jo Grimond to lend his support to the government - even with parliament balanced on a knife edge Liberal attempts to win influence were ignored.
As the months passed, Labour's grip on power tightened, and with a surprisingly solid swing towards the government in a by-election in early 1966 Wilson decided the time was right for Labour to gamble on winning a solid mandate.