Smith: Intimidation will not work

Reporting to MPs on the failed car bombings in London and Glasgow, Ms Smith confirmed that a "fast-moving" investigation was under way.

The police had "substantially stepped-up protective security measures," including greater use of stop and search powers. These measures were designed to "maximise public safety while minimising disruption to normal life".

Ms Smith paid tribute to the vigilance of those who helped avert major explosions in London and at Glasgow Airport.

She said: "It is through our unity that the terrorists will eventually be defeated. The fact that people have been prepared to go about their lives as normally as possible this weekend sends the strongest message to those who wish to destroy our way of life and our freedoms that we will not be intimidated by terror."

Ms Smith was flanked by Prime Minister Gordon Brown and key Cabinet colleagues as she outlined the discovery of the two car bombs in London and the driving of a Jeep into the entrance of Glasgow Airport.

She confirmed that six people had been arrested and a seventh was critically ill in hospital following the incidents, which police had confirmed were linked and could have caused "significant" loss of life. And she disclosed that searches had been carried out in at least 19 locations, as part of the "fast-moving investigation"

To cheers of support, Ms Smith thanked all those involved in response to the incidents, particularly the ambulance crew whose vigilance helped spot the first car bomb and the explosives officers who manually disabled the device.

The police had responded with high visibility patrols, including armed response vehicles, and increased physical protection aground airport terminals.

Police Counter Terrorism Security advisers had already given security advice to a range of "crowded places" in recent months, including over 450 major sporting venues and around 400 shopping centres.