The former US central bank chief, Alan Greenspan, has agreed to become an honorary adviser to the UK Treasury – less than seven hours after his 19-year tenure as Federal Reserve chairman ended.

Gordon Brown said Greenspan would assist the Treasury in developing its ideas about dealing with global economic change. His role will involve regular meetings and exchanges of papers, but no pay cheque.

“This is an unexpected appointment to say the least,” said a Treasury civil servant. “Greenspan has previously praised Brown as being ‘peerless’ among the world’s economic policymakers, so there’s a lot of respect there.”