Britain unveils the first of its spending cuts tomorrow - the harshest package since World War II - but counter-terrorism and cyber attack prevention are among areas expected to get funding boosts.

Terrorism and cyber warfare have been identified as the two most serious threats facing Britain, and a higher priority than preparing for another international military conflict, according to Britain's national security strategy - a detailed plan that spelled out the country's security priorities today.

The announcement comes just days after the head of Britain's eavesdropping agency, GCHQ, warned of the threat that cyber attacks pose to the country's computer infrastructure. Iain Lobban said 20,000 malicious e-mails had been detected on government networks each month, and significant disruption had already been caused by electronic worms.

Preventing another attack like the 2005 suicide bombings that killed 52 London commuters is also a top priority. US and British intelligence officials say a credible European terror plot is still active and being monitored.

"While military spending on big ticket items like jets and tanks will probably be decreased, it is true that we will likely see spending hikes in cyber attack and terror prevention," said a British government official who spoke on condition of anonymity because he was familiar with the spending cuts but was not authorised to speak to the media.

Today's strategy set the scene for tomorrow's Strategic Defence and Security Review, which will detail areas to be sacrificed to achieve the 7 per cent to 8 per cent savings demanded by Britain's treasury.

Overall spending cuts will be announced Wednesday where government ministries are likely to see their budgets reduced by up to 25 per cent over four years - far more than any other British administration since World War II has attempted, even under former Prime Minister Margaret Thatcher.

Home Office Secretary Theresa May said today efficiencies were possible without sacrificing security.

Another British official who was also aware of the cuts but spoke on condition of anonymity because of the sensitivity of his job, said staff reorganisation had already provided some savings.

Britain's cuts have raised questions of how it will be seen on the world stage, and more specifically what it means to its participation in the NATO-led military operations in such places as Afghanistan. (AP)