The 2005 election (and how distant Michael Howard's campaign seems now) led the Conservatives to learn not to talk about immigration, welfare reform or Europe, a lesson Cameron has applied effectively. But four years is an eternity in politics. Immigration and welfare reform are now respectable subjects of debate, and it is Labour who are increasingly being seen as the nasty party in their efforts to capture the readership of the Daily Mail. Only Europe remains out of bounds as a subject of open Conservative debate.
If I were Cameron, I'd be inclined to leave things as they are. So natural Conservatives like me are going to vote UKIP in June for the European elections? So what? This should not be a reason for Cameron to declare a harder line on Europe if this would mean losing anti-Labour votes.
The best line to take is the one emerging at the moment; we're all equivocal on Europe, but Labour are slavish and devoted Europeans. Vote for whoever you feel comfortable with, just so long as it's a vote against Labour.