Back in 1974 public opinion polls consistently showed that 70% of Conservative voters supported electoral reform
Following the formation of the 2010 coalition government, recent polling attitudes are still in tune with 1974. In a recent ComRes poll voters were asked about attitudes towards first-past-the-post:
The first-past-the-post system for elections to the House of Commons should be replaced by a system that reflects more accurately the proportion of votes cast for each party.  
Agree            78%  
Disagree        18%  
http://www.comres.co.uk/page1901674249.aspx
Voters were asked about their attitudes to their voting intentions for a referendum on the electoral system. Latest polling (June 19 th) from UKPollingReport states:
Voting intention for the referendum on switching to Alternative Vote currently stands at YES 44%, NO 34%, wouldn’t vote 5% and don’t know 17%. A lead for alternative vote, but not a particularly large one. Prior to the question wording being decided, the yes and no campaigns being organised, and the public being exposed to many arguments for or against AV, I think we can only conclude that the referendum could easily go either way whenever it is called.
http://ukpollingreport.co.uk/blog/archives/2720