UK terror threat 'still serious'

Fencing could be electrified around Big Ben

The Home Office says the threat of terrorism in Britain is "real and serious", after a new warning of possible al-Qaeda attacks in the US.

The US Homeland Security department said intelligence showed a "credible threat" against targets in New York, Washington DC and New Jersey.

The security alert there had been raised to the second highest level.

The Home Office said the threat to the UK was under review, but would not say which security level is now in effect.

"We keep our threat level under constant review. If a specific threat arises we would review our levels accordingly," said a spokeswoman.

"If the public need to take specific action, we will issue advice and information immediately. We still say the threat remains real and serious."

She said agencies remained at a heightened state of alert.

Big Ben

The warning of attacks on US landmarks comes as a newspaper report suggests authorities are considering putting an electric fence around Big Ben.

The report in The Times said strengthened fencing, possibly electrified, would be set up around part of the House of Commons perimeter.

It said other measures being considered were diverting traffic from the area, to prevent a potential car bombing, and floating booms in the Thames to protect the Palace of Westminster from an attack from the river.

In March, two Greenpeace demonstrators climbed Big Ben in a protest against the Iraq war.

They said at the time that beating the defence around Parliament was "easy".