MI5 director general Jonathan Evans also warned that some terrorist groups would be considering whether they could launch an attack on Britain during this summer's Olympic games.
The Games present an attractive target for our enemies and they will be at the centre of the world's attention in a month or so.
No doubt some terrorist networks have thought about whether they could pull off an attack.
He insisted the Games were not an easy target, but added that there was "no such thing as guaranteed security".
All leave has been suspended at MI5 to ensure the service has its full complement of some 3,800 staff for the Olympics, double the number it had a decade ago after the September 11 terror attacks.
More top news
A mass inhalation of "hippy crack" was carried out in the shadow of Parliament on Saturday in protest at the Government's drug policy.
Declan Donnelly is reportedly tying the knot with his manager partner Ali Astall in Newcastle today.
Warming up in the south but with breezy showers across Scotland today.