Britain is on its highest ever state of alert amid fears of more attacks following last week's bombings in London's transport system which killed at least 49 people, The Times newspaper said Monday.

Security services, the military and police were on "severe specific" alert, as British intelligence believes the bombers did not die in the blasts on three subway trains and a London bus but survived to plot further outrages, the paper said.

On Saturday, Andy Trotter, the deputy chief constable of British Transport Police, said it was "perfectly possible, given the attacks of Thursday, that terrorists could strike again."

Investigators have been studying the similarities of the attacks with last year's Madrid train bombings, during which four trains were targeted in three railway stations, the explosions going off within minutes of one another, just as in London.

The Times quoted a senior intelligence source as saying it was believed that the bombers traveled into King's Cross together before splitting up to create mayhem on the Circle and Piccadilly lines.

Investigators are examining closed circuit television footage of the stations hit and have also appealed to passengers to send in any mobile telephone video or still images which they happened to have taken within seconds of the devices going off.

According to a senior police source, "the pattern of these attacks is that the masterminds make sure they are well clear before the bombs explode."

Source: Xinhua