Stephen Byers has admitted that he ignored a warning that announcing details of the London Underground PPP would undermine contract negotiations with the private sector.

The transport secretary was warned by London Transport chairman Sir Malcolm Bates that revealing the details would undermine the public sector's negotiating position because the bids were "not firm".

Appearing before the Commons transport committee yesterday, Byers said he had decided to publish the information because he had promised the Commons he would do so. "I have a responsibility to this House," he said.

He also revealed that the rate of return for the private companies would be higher than previously indicated. The rate could be over 20 per cent, compared to around 15 per cent in other PFI contracts, he said.

The minister also told MPs that the 10 year transport plan was not "set in stone" and said he did not accept claims that the city was going cold on the concept of public/private partnerships.

The FT reports that some ministers privately believe the row will cost Byers his job.