Roughly when Hell freezes over. There is no support for it in the Conservative party, the Lib Dems are not going anywhere, except maybe backwards, and opinions are divided within the Labour party, and the Media.

The general public are strongly against it, and without a united campaign from the media and politicians would never support it in it's current state. Maybe in a decades time, when Southern Europe's economy stop resembling third world countries, there is some chance.