Computer networks controlling electricity supplies, telecommunications and banking are being attacked thousands of times a day in a new cyberwar against Britain waged by criminals and terrorists — some of them backed by foreign states — the Government has said.

Lord West of Spithead, the Security Minister, told The Times that a mixture of state-sponsored individuals “and those operating at a terrorist level” frequently tried to break into the key networks.

Intelligence organisations such as MI5 have given warning of the threat of state-sponsored “cyber-espionage” from countries such as Russia and China, but this is thought to be the first time that the Government has quantified the extent of the threat to the nation’s networks, furthering the prospect of more widespread computer-based “warfare”.

“If you take the whole gamut of threats, from state-sponsored organisations to industrial espionage, private individuals and malcontents, you’re talking about a remarkable number of attempted attacks on our system — I’d say in the thousands,” Lord West said. “Some are spotted instantly.Others are much, much cleverer.”

Security experts in the US said that they had uncovered evidence of Russia having carried out state-sponsored cyberwarfare against Georgia by attacking government computer networks during the recent conflict.

Lord West said that the most serious threat was from terrorist-backed hackers trying to break into and manipulate networks such as National Grid’s, which were heavily reliant on computer systems. Other corporate networks, such as those of defence companies, were also at risk.

National Grid, BT, and Thames Water all declined to comment yesterday, citing security reasons, though National Grid said that it had “robust systems” in place to protect its infrastructure, and worked closely with government security services.

Security experts said that any successful attack would be likely to result from a hacker exploiting the part of a computer system that was connected to the internet — known as a port — and raised concerns that British companies were not doing enough to protect their networks.

“We’re building this house of cards at the moment — connecting elements of our financial systems, as well as the systems which control nuclear power or water distribution, to the internet, and it’s a very open environment,” said Earl Zmijewski, an analyst with Renesys, a company that monitors internet traffic. “I can launch an attack on you from anywhere.”

Paul Vlissidis, an analyst with the Manchester-based security company NCC Group, said: “Most companies are not aware of the threat, and have an unreasonable faith in their own security systems.”

SecureWorks, an Atlanta-based company, said it had discovered communications suggesting that computers associated with Russian state-owned organisations called on known web-based criminal gangs to attack Georgian government networks hours before airstrikes began nearly two weeks ago. Lord West said that he could not comment on the claims.

The Russian Government admitted that individuals based in Russia might have been responsible for the attacks but denied involvement. “It is nothing but the demonising of the Russian Government,” Dmitri Peskov, a spokesman for Vladimir Putin, the Prime Minister, said.

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