Growing cyber attacks by terrorists on government computer systems in Britain could be "the next Pearl Harbor", the head of the country's Intelligence and Security Committee (ISC) has warned.

Ahead of a government report that lists cyber attacks alongside violent terrorism as the most important challenges faced by the country, Sir Malcolm Rifkind, chairman of the ISC, said cyber attacks could pose "very massive problems".

"It's not people hacking into private citizens' computers. What we're talking about is terrorists being able to actually use cyber methods, for example, to interrupt the National Grid to prevent proper instructions going to power stations, which are under computer control," he told a BBC Radio 4 programme.

Referring to the 1941 attack on Perl Harbor, Rifkind said that's "the kind of severity that could happen if we don't get it right."

The attack on US naval base at Pearl Harbor, Hawaii, was a surprise military strike by the Japanese Navy that prompted the US to declare war on Japan resulting in their entry into World War II.

Rifkind's claim comes as a Government report called the National Security Strategy identifies the "growing threat" of computer hackers to Britain as a key priority for the security and intelligence services.

The primary threat remains al-Qaeda in Pakistan and its associates in Somalia, Yemen and North Africa, who continue to plan attacks against targets in Britain, the security strategy will say.

The report, to be unveiled by Prime Minister David Cameron, puts cyber attacks ahead of natural disasters and military attacks from other countries in a list of the four most pressing concerns to national security.

The report is said to be a key precursor for the Strategic Defence and Security Review, which will explain how Britain will defend itself against such attacks.

It will also form the basis for spending decisions to be announced this week, including a 500-million-pound boost to cyber defence, The Daily Telegraph reported.

That is likely to mean that British intelligence agencies MI5, MI6, GCHQ and the Metropolitan Police counter-terrorism command will escape the worst of the cuts.

But the document will also highlight the threat from cyber attacks on government infrastructure.

While not naming individual states, GCHQ, which is responsible for cyber defence, has been concerned for some time that states such as China and Russia are unlikely to use conventional or nuclear weapons in an attack on Britain and are more likely to attempt to shut down essential systems used to run the country.

Similar attacks have been seen when Russia has been in disputes with Estonia and Georgia, leading to problems with their Internet and even cash machines.