Labour is poised for a possible leadership contest as soon as this summer ahead of a set of local elections which are expected to be a bruising experience for the party. If Sir Keir Starmer is forced to stand down – either in the coming weeks, or at another point before the next general election – Angela Rayner is seen as a frontrunner to succeed him. The former deputy prime minister has made it clear that she is backing Starmer. But she has als…