So here's the deal. John Major, more than any other person, got us into this mess. He signed the Maastricht Treaty which massively eroded UK sovereignty, while giving the British people no vote in the matter. Before Maastricht, there was a minority of opponents of Europe. Afterwards, opposition grew, but never had the opportunity of a vote, until Cameron gave us one.
So Major is battling for the wisdom of his own judgement and his responsibility for forcing us into an imperial Europe.
For myself, I think he looks like a plausible man, but he doesn't know much and is the example of much that was wrong with the conservative party post-Thatcher. No one has forgotten he also had an affair with perhaps the least charming MP of his generation, whose name was Edwina Currie.
He and Blair are the two ex-PMs telling people not to vote for their old party. Major was a conservative PM. Blair was a Labour PM. I don't think many people like or follow the advice of either of them.