Gordon Brown was guilty of misusing the powers of the prime minister when he took a politically motivated trip to visit British troops in Afghanistan, Jack Straw has said.
The former justice secretary, who served in both Tony Blair and Gordon Brown's cabinets, told BBC Radio 4 on Thursday morning that he came to realise Brown had a "remarkable propensity for double-think and disingenuity".
And he criticised him for a "paralysis" of decision making in 2007 when he failed to shut down speculation that he would call a snap general election until it was too late.
Straw said Brown's attempt to then take media attention away from the Conservative Party conference was also a big mistake.
"He went off to Afghanistan in a flat footed, ridiculous attempt to draw attention away from the Conservatives, it was a misuse of the powers of the prime minister," he said.
And Straw, who ran Brown's leadership campaign, said he had seen little point in standing for the top job himself. "What would have been the point of standing when you were just going to get crushed?"
However Straw's criticisms were not confined to Brown. He also said he "never approved" of the way Tony Blair ran the government.
"I owe Tony a huge amount, he essentially made my career," he said. "I would not have run cabinet in the way Tony did."