Tony Blair lost another long-standing aide yesterday when his senior economic adviser quit to take a job in the private sector. Derek Scott, 56, is to be an economic consultant with the accountancy group KMPG.

He had been at No 10 since Labour's 1997 general election victory, but in recent months his relationship with Gordon Brown, the Chancellor, had become strained.

Mr Blair has also lost Alastair Campbell, his director of strategy and communications, and Jeremy Heywood, his principal private secretary, from his inner circle since the summer.

From 1976 to 1979, Mr Scott was a special adviser to Denis Healey during his tenure as Chancellor and subsequently to the former prime minister James Callaghan, when he was leader of the Opposition.

Before 1997, he combined working with Mr Blair with the post of director of European economics at BZW.

Mr Scott will advise KPMG mainly on international issues on a part-time basis.

Mike Rake, KPMG International's chairman, said: "Derek Scott has a first-class record as an international economist and will be a valuable addition to our international capability."

The only person to have remained in Mr Blair's team since 1997 is Jonathan Powell, his chief of staff. But he too is rumoured to be looking for another job.

David Miliband, the former policy head at Downing Street, is now an Education minister and Anji Hunter, the Prime Minister's "gate keeper" and a close confidante, left to join BP in 2001 as the oil company's director of communications.

Mr Campbell's partner, Fiona Millar, stepped down from her position as Cherie Blair's adviser in the summer.