Prime Minister Cameron firmly saying no to EU Zero took quite a few people by surprise, I didn't really think he had it in him. But Merkel and Sarkozy have gotten most of the EU on board. The Swedes and the Czechs (barring referendums) may be joining the UK in holding out, but for now long?
A change of government in the UK will put the Laborites squealing that Cameron has isolated them from the rest of Europe into power and how long will the resistance last then. Like all international orders, the EU has thrived by waiting around for governments decadent enough to join or fail to resist. Once you're in, getting out takes more guts than any government has shown so far.