In reply to Indy:
Interesting report on Newsnight last night about the reaction in Brussels. Quite a lot of hostility from France and Belgium and from J-C Juncker personally and a clear impression that there would be no going back if Art 50 was invoked. The francophone contingent will jump at the chance to regain influence with the perceived dominance of the Anglo-German axis gone (who said nobody listened to us in the EU?). There's also a move to abandon English as an official language of the EU.
The statement on the Commission's website at the moment is pretty unambiguous:
"As agreed, the “New Settlement for the United Kingdom within the European Union”, reached at the European Council on 18-19 February 2016, will now not take effect and ceases to exist. There will be no renegotiation."
That said, Juncker isn't universally popular either and the Poles (ironically) are pushing for a reform pressure group within the EU. Germany is sitting on the fence, and not only because of the cars they sell us.