International terrorism and cyber attacks pose the biggest threat to British security, a new government strategy published today said, ahead of a major shake-up of the defence budget.

The risk of a major accident or natural hazard, such as a flu pandemic, or an international military crisis between foreign states into which Britain might be drawn were also judged to be key threats facing the nation today.

They were outlined in a new national security strategy drawn up by Prime Minister David Cameron's coalition government, which took power in May, ahead of a major review of all public spending being unveiled Wednesday.

The review, intended to find billions of pounds in savings to help pay off the country's record budget deficit over the next five years, is expected to see the defence ministry's budget slashed by seven or eight percent.

Further details of exactly where the savings will be made are expected in a defence and security review Tuesday.

Today's strategy outlines three tiers of threats, the seriousness of which will be linked to the amount of resources allocated to dealing with them.

In a joint foreword to the strategy, Prime Minister David Cameron and Deputy Prime Minister Nick Clegg said Britain was entering an "age of uncertainty."

"This strategy is about gearing Britain up for this new age of uncertainty -- weighing up the threats we face and preparing to deal with them," they wrote.

"As a government, we have inherited a defence and security structure that is woefully unsuitable for the world we live in today. We are determined to learn from those mistakes and make the changes needed."