The Metropolitan Police has called on Londoners to make the capital a more hostile environment for terrorists.

Force chiefs unveiled a month-long campaign on Monday under the slogan "If you suspect it, report it", in a further ratcheting up of speculation over a possible attack.

The move followed commissioner Sir Ian Blair's warning last week that a series of forthcoming events this year make an al Qaeda-style strike on Britain more likely.

The general election, royal wedding, G8 summit and the UK's EU presidency are all "enormous" targets, Sir Ian Blair said.

And deputy assistant commissioner Peter Clarke, head of the Met's anti-terrorist branch, added to the atmosphere of anxiety by putting Londoners on alert.

Radio, underground, and newspaper adverts will all be used to drum home the message that "communities can defeat terrorism".

Vigilance

"We are asking Londoners for their help in reporting suspicious bags or packages, as well as encouraging them to think about anything or anybody that has struck them as unusual in their day-to-day lives," Clarke said.

"The focus [of the campaign] is to encourage the public to be vigilant and to contact police with any suspicions," he added.

"The first strand urges the general public to be aware of their surroundings, with posters urging people to look out for unattended or suspicious bags or packages."

London, and particularly the tube network, has been considered a prime target for terrorists to strike ever since the 2001 attacks on New York and Washington and last year's Madrid train bombings.

Security will also be at an unprecedented level for July's G8 summit in at Gleneagles in Scotland, while key EU meetings could be moved to Brussels to avoid creating another high profile opportunity.

The prime minister is facing increased restrictions on his movements during the election, despite his strategy of talking to voters directly rather than through the media.