Many people have heard the stories of middle class rural folk being confronted by inner-city deprivation and poverty, poor city kids who'd never seen a live cow before and lived in slums being fostered with wealthier people in the country etc.
I always kind of assumed that this must have led to some calls for societal change, i.e via a welfare state
Are there proven political effects from the evacuations?
There was not any major change in 1945 to established voting patterns in terms of social class, but there were key changes to WHO voted and WHERE they voted. The armed services registered in large numbers to vote and they overwhelmingly backed Labour, but that did not account for the dramatic swing around the country as their votes were spread across constituencies. However, working class urban conscripts and volunteers who did not go to war, those who were sent to rural areas to help with tasks such as farming, did have an impact. When we compare the results in rural constituencies for each election 1945 sticks out like a sore thumb - and this can be accounted for by the fact that sufficient numbers of traditional Labour voters voted in rural constituencies - rather than in their home constituencies - to swing many seats.
You may have heard people complain about the electoral college in the US, the fact that a rural vote effectively counts for more than an urban vote because of the population density inequality of constituencies, in a way the 1945 UK election was a social experiment in what happens if you take lots of Urbanites and get them to vote in the Rural areas. The impact of this was all the greater because many rural constituencies were still very small and could be swung by a small influx of voters.
The other major factor was WOMEN, those over 21 had been granted the vote in 1928 and it's from this point that the Labour Party becomes a credible force in UK elections - women of all classes voted Labour in greater numbers than their male counterparts, just as women in the US vote Democrat in greater numbers - and this has held true since Women's suffrage. The inclusion of women in the workforce during the war was also reflected by their greater political activity, including voter registration.
There were numerous other compounding factors such as the association of Churchill with both the Liberal and Conservative Parties and with hung Parliaments and coalitions - he was viewed by many as being a National Leader rather than a Conservative leader. The Conservatives arguably relied too heavily on being 'rewarded' for Victory and did not campaign as actively as Labour, they also went in for either scaremongering or cautionary tales, depending on your view point, likening Labour's socialism plans to Totalitarianism (ref. Churchill's so called 'Gestapo speech') which did not go down well with a Population who largely felt that the governments of the inter war years had reneged on obligations to care for people, especially veterans and war widows and orphans, after WWI.
If you want to read more about the 1945 election generally here's some resources
http://www.bbc.co.uk/history/worldwars/wwtwo/election_01.shtml http://www.spartacus.schoolnet.co.uk/GE1945.htm http://news.bbc.co.uk/1/hi/uk_politics/vote_2005/basics/4393271.stmh http://www.theguardian.com/politics/2001/mar/14/past.education http://en.wikipedia.org/wiki/Women's_suffrage_in_the_United_Kingdom http://www.iwm.org.uk/history/1945-general-election# http://news.bbc.co.uk/1/hi/uk_politics/4713041.stm