Pressure is mounting on Stephen Byers to sack his top political adviser for sending an email within an hour of the New York terror attack, suggesting it would be a "good day" to "bury" bad news stories.

Jo Moore, Special Adviser to Mr. Byers, sent the memo to civil servants and a policy adviser in his Deprtment of Transport, Local Government and the Regions.

It read: "It's now a very good day to get out anything we want to bury."

After its contents was revealed in a newspaper, she today issued an apology.

"I would like to sincerely apologise for the offence I have caused. It was wrong to send the e-mail and I accept responsibility for doing so."

The memo was sent to the then director of communications at Mr Byers's Department for Transport, Local Government and the Regions, who has since left his job. It was copied to other civiil servants.

Yet although she has been given a "severe reprimand" by Mr Byers, according to Downing Street, she has kept her job - with the backing of Tony Blair.

The Prime Minister's spokesman told reporters that Mr Byers accepted Ms Moore committed an "error of judgment but equally has valued Jo Moore's skills and experience."

But the spokesman was pressed repeatedly about controversial announcements made since September 11, such as the decision revealed on Sunday to allow Railtrack to collapse without shareholder compensation, and the go-ahead last week for the new Mox reprocessing plant at Sellafield.

The spokesman defended the timing of both decisions - saying they had to be announced about now anyway. "There is no link between the Railtrack decision and this memo," he said.

However it was revealed that Jo Moore herself was involved in contacting media organisations over the announcement.

The spokesman was also asked repeatedly why Mr Byers had not sacked Ms Moore for "appalling cynicism."

Several questioners pointed out that the incident would fuel the public feeling that Government decisions were made cynically.

The spokesman repeatedly stated that the memo had been "a mistake", and that despite the changed atmosphere of the international crisis and the war against terrorism, "normal decisions have to be taken.

There has not been a sudden rush of decisions."

Politicians joined in the attacks on Ms. Moore.

Tory Transport spokeswoman Theresa may said the email showed "a disgracefully cynical attitude by Government spin doctors."

Lib Dem Transport spokeman Don Foster said: "the rest of us were absolutely transfixed and horrified as we watched our TV screens, and the thought that there was someone working in the public services, thinking only how to bury bad news....is frankly horrific."