Adrian Montague, who is in charge of the Treasury's PFI Taskforce, had been canvassed about staying on for a further year. But he is thought to have decided to leave when his two-year contract expires in August.
His departure would leave a questionmark hanging over the future of the entire taskforce. Its other 10 members, all drawn from private industry and finance, are also on two-year contracts which end this summer.
A wide-ranging review of the PFI conducted by the chairman of Pearl Group, Sir Malcolm Bates, is due to be delivered to the Chancellor before next week's Budget.
Mr Bates, who carried out the first review of the PFI shortly after Labour came to power, has been asked to examine how well the PFI has performed, the extent to which it is fully bedded down and what new institutional arrangements should be made when the taskforce reaches the end of its term.
Since Labour took office, a further pounds 4bn worth of public projects have been financed through the PFI, bringing the total value amount of private capital raised to pounds 11bn. The aim is to get a further pounds 3bn worth of projects financed through the PFI in each of the next three years.