T here aren’t many good jokes about politicians, and fewer suitable for publication, but one doing the rounds in Westminster should provoke a wry smile. Goes like this: “A Blairite, a Brownite, and a Corbynite walk into a bar. The barman says: ‘What are you drinking, Andy?’”. It’s funny because it’s true, as they say, and it gets directly to the essence of Andy Burnham ’s great strength and his great weakness as a prospective replacement for Sir Keir Starmer . The attraction is that he is one of politics’ more flexible players, and his supporters can read what they will into current vague lefty vibes. The negative is that his record suggests he might not be any more devoted to principle than the openly pragmatic Keir Starmer. Sir Keir Starmer, Andy Burnham and fellow leadership candidate Angela Rayner meet pupils during a visit to a school breakfast club ((Paul Ellis/PA)) No one, however, doubts his ambition for the premiership, even though it has taken him on a circuitous route - via the North.…