Why is this dangerous?
Stop pandering to UKIP defectors
This whole debate is essentially giving the playing field to UKIP. A minor party that gets an obscene amount of media coverage. A party that has no elected MP, but gets infinitesimally more media coverage than a party that does (the Green Party). There is a debate about European immigration right now, we get that. But I'm dumbfounded by every single party's determination to give the centre ground to UKIP, from whom all other policies flow.
Which leads me onto my next point...
Stop sending mixed messages
"We want a referendum but we want to stay in Europe really, honest". Are we supposed to follow on your words with such a weak, half-hearted policy? When someone votes for a UKIP candidate, they know they are voting for a withdrawal from the European Union. If I vote for your party, I want it to be a vote for staying in the European Union. No ifs, no buts. If it is your policy to stay in the EU, my vote for you should be my way of expressing that. The public has had its say. There is no need for a referendum.
In fact, this is one of the chronic problems of the major parties today; they seem to be unable to create an coherent policy on any issue that really matters. "We want to stay in the EU, but we'll have a referendum anyway" is one hell of a mixed message. Exactly how much do you want to stay in the EU? I'm not convinced as to your commitment to that policy. At least when people vote for UKIP they know what mandate they're voting for, exactly.
Stop being idiots
Every time you create a reactionary policy to UKIP's, you give their position credibility. Stop it.