Steven Fielding's What Did 'The People' Want?: The Meaning of the 1945 General Election is a fairly good analysis of what caused the Labour government, in particular because it partly lessens the easy, common analysis which some tend to make about the 1945 election; that the people had been radicalised by the war to demand a better lot.

With regards 1951, it's worth acknowledging the 1950 election which despite losing a large number of seats, Attlee's government still had a parliamentary majority of 5. Attlee's government had made several honourable strides, but the fact was that several members of his cabinet were at each other's throats and the political situation was volatile. As recent British Prime Ministers would squirm at the thought of, a majority of 5 was small in that time, too small enough to function in the legislature. This was reinforced by the fact that a lot of Labour ministers couldn't devote their entire time to the lobby because they spent a lot of time in hospital - including the Prime Minister himself. These tight conditions were enough for George VI to request a snap election be called by Attlee, which Clem obliged to.

But there were a range of 'reasons' why people might've chose the Conservatives in 1951. Attlee had formed a post-war consensus, based on Keynesian policies and a welfare state and the Conservatives made great effort to persuade the electorate that they would not repeal the progress Attlee made (and this was partly the case - there were smaller nationalisations such as the profitable steel and aluminium industries and the Conservative government in some cases went even further - a notable example is the greater amount of houses they built).

Despite being a real bone of contention among the left and right of the Labour Party in Britain today, Attlee was without doubt a card-carrying Atlanticist so to speak, and committing himself to the costly intervention in Korea was perhaps his biggest mistake. The cost of rearming was severe, and in 1951, it was being proven that when it came to the welfare state and rearmament, it was one or the other and not both. Hugh Gaitskell, Attlee's then third Chancellor of the Exchequer, was unenviably charged with finding the money to rearm and eventually this would be taken from the NHS - with charges for dental care, prescriptions and glasses - causing a very public row with Health Minister Aneurin Bevan which resulted in his and two other ministers' resignations.

To me, it would seem that internal problems in the government were the main reason for its eventual collapse, given the Conservatives were offering a broadly similar programme to theirs. I absolutely do not envy your research. I did this for one of my high school assignment and it was pretty excruciating trying to find a fair and balanced analysis of this time in British political history.

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