However the political parties usually back a specific line on Europe and will be involved in a yes/no vote. Given the political stances of the parties, this is how I expect the MPs to vote and encourage the public to vote. Labour are mostly pro EU, the Libdems, SNP and Plaid Cymru are very pro EU. The Conservatives are very mixed on EU membership. I believe a lot of this posturing by Cameron is because the Euroskeptic wing of the Tories are emboldened to push for this. Think of it being like Tea Party Republicans, except more reasonable on matters not on Europe. Given the fiscal mess that is the Eurozone the anti-EU people are spreading a bit of FUD around. Of course in a referendum campaign non-politicians will be very much involved, especially celebrities. Also businesses will most likely go for a yes vote and put money into the 'yes' campaign - I think the City (London banks and financial businesses) are very pro EU. I don't know how a 'no' vote would be funded - I guess a few very wealthy people plus UKIP (UK independence party IMO like the tea party proper but in their own actual party) would be leading the way. I think BNP would be anti-EU but they will be not very vocal about it given their extreme nature on racial issues. When an actual referendum comes I believe a lot of people who are saying in opinion polls that the UK ought to be out of the EU will change their position. Especially when the bulk of trade outside the UK is to EU countries, and there being no guarantee that a non-EU UK would be accepted into a free trade agreement... that alone should get most of the yes votes on board.