It was an error to leave but this does not mean that it would be a good idea to go back in. What would make sense is further alignment with the bloc; economically beneficial all around and would not cause political difficulties, at least not for a Labour government. The present state of affairs benefits precisely no one.
This.
Business want it and when business is happy with it, there's nothing much the Tories can do about it.
Labour did this with a whole raft of legislation in 1997-2001 when we were still in the EU to align ourselves with the market (including the minimum wage.)
Poll
