The chief executive of Partnerships for Schools has resigned to become boss of transport firm National Express

The government's £40bn Building Schools for the Future programme was thrown into confusion this week after the man charged with delivering it quit after eight months in the job.

Richard Bowker, the chief executive of Partnerships for Schools, the organisation running BSF, will leave at the end of July to become chief executive of transport company National Express.

His salary will more than double to £450,000 a year compared with the £200,000, plus £50,000 in bonuses, he received at Partnerships for Schools.

A successor to Bowker has yet to be appointed, and his departure comes as speculation mounts that the BSF programme has been delayed. Although four schemes have appointed a preferred bidder, none has reached financial close.

Bowker denied that there had been delays. He said: "I don't accept that. It's true that we're a few months behind on the financial close of the first one, I accept that. But we had to get that right."

He said that his departure was the result of a once-in-a-career opportunity and not because of BSF. "I would have liked to have seen it further along, maybe for a couple of years, but I just couldn't have turned this opportunity down. It is not a signal or message about BSF."

Two months into his role at Partnerships for Schools, it was speculated that he was being interviewed for the Olympic Delivery Authority, which he declined to comment on at the time.

Bowker was in charge of a programme to deliver 3500 secondary schools in 13 years. In an interview with Building last month Bowker said that 10 projects were likely to have reached financial close by next March.

A consortium led by Skanska was appointed preferred bidder at a Bristol scheme last year; this was supposed to have reached financial close but has yet to do so.

News of Bowker's departure shocked the industry and education sector, and some reacted with dismay. Mark Gordon, construction director at Costain said the decision would lead to questions about BSF. He said: "Bowker provided BSF with some leadership, stature and drive. The question is why has he left - is it for his career, or does he know something we don't?"

Ty Goddard, chief executive of School Works, said: "This so-called safe pair of hands did not last very long. It leaves a potential leadership vacuum at a crucial stage."

Shipbuilding company VT Group has unexpectedly been selected as preferred bidder by Greenwich council in London for its £290m Building Schools for the Future programme.