Keir Starmer has seen off a major Labour rebellion over a bid to force a parliamentary investigation into his appointment of Peter Mandelson , but many of his own MPs warned he was running out of political capital. After Downing Street deployed its full weight to force Labour MPs to block a referral to the privileges committee over the scandal, some angrily accused Starmer of leaving them facing accusations of a “cover-up”. Previously loyal MPs warned the prime minister to tread carefully, particularly after what are expected to be a damaging set of election results for Labour next week.…