An online war has begun between Britain and terror groups and enemy states, with the country facing a serious threat to its national security from cyber attacks, a top official of a spy agency has claimed.

Iain Lobban, the Director of the Government Communications Head Quarters, has said that Britain is forced to fend off 1,000 cyber attacks every month.

In the first public speech by the head of the intelligence agency, he described the threat to the critical national infrastructure like power stations, water plants and air traffic control as "real and credible".

"Worms" deliberately targeting government systems have already caused "significant disruption", he was quoted by 'The Sun' as saying.

Meanwhile the rate of cyber attacks is growing by a frightening 60 per cent every year, with e-crime costing the economy "well into the billions".

Lobban, whose Cheltenham-based GCHQ eavesdrops on radio, phone and email communications, told the International Institute for Strategic Studies in London: "Cyberspace is contested every day, every hour, every minute, every second.

"I can vouch for that from the displays in our own operations centre of minute-by-minute cyber attempts to penetrate systems round the world.

"We have seen worms cause significant disruption to government systems -- both those targeted deliberately against us and those picked up from the internet accidentally. There are over 20,000 malicious emails on government networks a month, 1,000 of which are deliberately targeting them."

The monthly rate of attacks to steal government secrets or money equates to one every 90 minutes. The cyber threat is also very real to Britain's economy and ordinary people's money, Lobban insisted.