The transport secretary has warned that more transatlantic flights may be cancelled because of security fears.

Following a series of terrorism alerts last week a number of British Airways flights to Washington and elsewhere had to be scraped.

And Alistair Darling said on Sunday that there will be more of the same before services can return to normal.

However he refused to comment on newspaper stories that the government had received intelligence information that al Qaeda, which was responsible for the September 11 attacks on New York and the Pentagon, was planning to use BA flights to launch strikes against prominent targets in the USA.

But the Cabinet minister confirmed that the cancellations, made by the airline on the advice of the government, were in response to specific intelligence.

"What I can say is that I fear that for many years to come, we are going to be living in an age where there is going to be a heightened state of alert," he told the BBC's Breakfast with Frost programme.

"Sometimes it will be quite severe, at other times perhaps less so.

"We are going to have to get used to increased security at airports. From time to time that will be noticeable and at other times maybe things will be going on behind the scenes.

"A decision to cancel a flight is comparatively rare. But where we have to cancel a flight, the grounds are very clear in our minds and we are justified in taking that decision."

Darling said in striking a balance between safety and needs of passengers and businesses, it was sensible to err on the side of caution.

"At the end of the day, we have got to reach a judgement based on the information we have as to whether, in extreme cases, a flight has to be cancelled or whether other measures would be adequate," he said.

"The first line of defence, and the best possible thing you can do is to stop somebody or stop something that you are concerned about getting onto an aeroplane.

"However, there will be cases - and they are comparatively rare - where it may be necessary to go further and to ground a particular flight.

"It really depends on the information that we have got."