Britain faces the threat of cyber attacks from hostile states and criminals which could damage its critical infrastructure, the head of the country's electronic spying agency warned Wednesday.

In a rare public speech, Iain Lobban said Britain's infrastructure -- such as power grids and emergency services -- was at increased risk as the rapid growth of the Internet made systems more vulnerable.

"The threat is a real and credible one", he told an audience in London at the International Institute for Strategic Studies.

"We already provide expert advice and incident response to the operators of critical services.

"We must continue to strengthen these capabilities and be swifter in our response, aiming to match the speed at which cyber events happen."

Some 1,000 malicious emails each month were already being targeted at government computer networks, said Lobban, director of the Government Communications Headquarters (GCHQ).

Britain's critical national infrastructure refers to services that are crucial to daily life. It includes mass communication, financial services, health and transport.

Lobban further warned Britain's economy could be at risk if effective protection against cyber attacks was not developed.

Putting such protection in place would help "the UK's continuing economic prosperity," he said.

"A knowledge economy needs to protect from exploitation the intellectual property at the heart of the creative and high-tech industry sectors."

The director conceded his comments came as ministers weighed their "spending priorities" -- the coalition government is poised to give full details of sweeping cuts to defence and public sector spending next week.

But the risk of cyber attack was not "solely a national security or defence issue," he argued.

"It goes right to the heart of our economic well-being and national interest."

GCHQ is one of Britain's intelligence and security agencies, alongside domestic intelligence service MI5 and foreign intelligence agency MI6.

GCHQ is more often associated with electronic intelligence-gathering but Lobban was keen to stress its role in protecting vital computer networks.