With just over five months to go until the Olympic Games, police in London have launched a new anti-terrorism hotline to persuade residents and visitors to stop potential attackers.

“Terrorists live amongst us. We want you to tell us about anyone or anything you see which is out of place in your normal day-to-day lives,” said Stuart Osborne, deputy assistant commissioner of Scotland Yard.

“We know you may have concerns about speaking to the police, possibly because your friends or family may find out. But you may well have information which could save lives,” he said on Monday

The force said the threat of attacks to London and Britain in general, whether from al-Qaeda inspired groups or individuals or Irish dissident republicans, was “real and serious”.

The confidential hotline will be promoted in a leaflet campaign and through adverts in local and minority ethnic newspapers, which will assure informants that any activity will be thoroughly researched before it is acted upon.

“We would rather take lots of calls which are made in good faith, but have innocent explanations, rather than not getting any at all. Not making that call could mean we miss out on a vital piece of information,” Osborne added.

About 25,000 troops and police will be deployed in London during the Games as part of a STG553 million ($A820 million) security operation that also includes warplanes, two navy ships and surface-to-air missiles.