McDonnell also plans to put green targets at the centre of all economic decisions

Treasury officials have been told to prepare for an emergency budget within 10 weeks of Labour taking power under party plans for a Corbyn government if there is a snap election.

John McDonnell, the shadow chancellor, has written to Sir Tom Scholar, the Treasury’s senior mandarin, to warn him that Labour would tear up government plans for a three-year spending review and replace it with five-year plans for spending in government departments.

The letter, obtained by The Sunday Times, details plans by the shadow chancellor to shake up the way the Treasury runs the economy and ensure it focuses on delivering Labour’s main policies, including nationalisation in the energy industry and other businesses. In what amounts to the most radical shake-up of a key department