The transport secretary is again facing opposition calls to come clean about when he decided to put Railtrack into administration.

Conservative shadow transport secretary, Theresa May, has demanded that an embattled Stephen Byers appears before the Commons to explain himself following the latest twist.

"The point of order on Thursday has called once again for Stephen Byers to return to the House and defend himself against mounting evidence that he lied to parliament over putting Railtrack into administration," she told this website.

"It seems increasingly certain that he made the decision weeks before it was announced, so not only did he lie to MPs, but he also created a false market in Railtrack shares."

May claimed Byers is now an obstacle to improving the railways and again called for him to resign.

"How many lives does this man have? Stephen Byers has lost the confidence of both the travelling public and the City, cutting off much needed private sector investment in our rail network," she said.

"So not only is Stephen Byers a liar, he is also a failed transport secretary. The British people deserve better, and for that reason alone he must go."

Liberal Democrat transport spokesman, Don Foster, also questioned Byers' statements to parliament and his reputation.

"There's no doubt Stephen Byers has become a serial misleader of parliament. Whether its over the funding national air traffic services, the resignation of Martin Sixsmith, money for Railtrack shareholders, even the future of county councils," he told the BBC.

Foster accepted that Byers had made his decision on October 5. He said issue was that he shared his thoughts with too many people in the days leading up to it.

"The real problem about this issue is that clearly there was a great deal of lose talk going on. Had it got out more publicly, and Pam Warren kept it quiet, it could have had a really devastating effect on the Railtrack share price," said Foster.

"The secretary of state should have been more discreet than he was."

Foster accused Byers of behaving irresponsibly.

"The decision he made was the correct one," he said. "I suspect that what happened was that the secretary of state rather wanted to gloat to Pam Warren that he was going to do something about a problem she was clearly deeply concerned about to score some brownie points off of her. A responsible secretary of state would have kept quiet."

The new row blew up after Paddington Survivor's Group chairman, Pam Warren, claimed that at a meeting with the cabinet minister on September 12 last year he told her that Railtrack "wouldn't be much trouble much longer".

The announcement that the troubled rail company was being placed in administration was made on October 7 and Byers told parliament the decision had only been made two days before.

Number 10 was again forced to issue a statement of support saying it did not recognise Warren's version of events and insisted that the prime minister was standing by the transport secretary despite the latest controversy.

A spokesman for the department of transport insisted that no decision had been taken at the time of the meeting.

"The crucial element here is that no decision had been taken at the time of this meeting. But we are not going to get into who said what to whom," he said.

But the department conceded that "various options" for the future of Railtrack may have been discussed at the meeting.

Although rail Warren concedes that Byers did not use the word "administration", she hit back at Downing Street claims of a misunderstanding.

"We know what was said at the meeting and we know we are telling the truth. We have notes to prove it, unless he's got a recording of the meeting stating differently, I don't see how he can call us liars, or not recalling proper," she told the BBC.

"He actually said to us, watch out for around October 8 or 10 when you will have some news that will be very pleasing to you."