LONDON — Andy Burnham’s allies have been plugging his credentials as a straight-talking communicator. He had a chance to prove it Thursday. The Greater Manchester mayor appeared on a special edition of Question Time — the BBC’s flagship political debate program — as he seeks to return to Westminster in the Makerfield by-election on June 18. The so-called “ king of the north ” faces a tough fight against the populist Reform UK, whose candidate Robert Kenyon was also on the panel.  POLITICO runs