Last week's historic Irish Republic Army renunciation of violence was greeted with relief by politicians here, but for ordinary Londoners it was vastly overshadowed by anxiety shrouding the city after the recent attacks.

"It's much more worrying. With the IRA you didn't feel scared every time you got on the tube," said pensioner George Burrows, buying a newspaper at King's Cross, scene of the deadliest July 7 bombing which left 27 dead.

The sense of fear in London -- where yellow fluorescent police jackets are everywhere, and armed officers commonplace -- is fuelled by repeated warnings that further attacks cannot be ruled out despite the wave of arrests last week.

The Sunday Times said a third terror cell was planning multiple suicide bomb attacks against "soft" targets in London like the Underground subway network, left reeling by the July 7 and July 21 attacks.

After the initial four-pronged suicide attack, which killed a total of 56, much was made of the fact that Londoners were not new to terrorism.

For years during Northern Ireland's "Troubles" lasting more than three decades, London got used to the regular blows of IRA attacks, including most notoriously the near-killing of prime minister Margaret Thatcher in Brighton in 1984.

But the July 21 attacks changed the mood here, underlining both that the bombings were not a one-off but above all that even a vast police presence could not prevent an alarmingly organised assault at the heart of the capital.

"A nightmare ends, another nightmare begins," said the Guardian daily after the IRA statement last Thursday. "It was if one flag was lowered while another was raised," said Jonathan Friedland in a front-page commentary.

The differences between the IRA terror threat and the latest bombings, claimed by offshoots of Osama bin Laden's al-Qaeda network, are legion.