The military will also immediately retire its flagship aircraft carrier, HMS Ark Royal, as the government slashes budgets.

Defence Secretary Liam Fox insisted the cuts will not affect combat operations in Afghanistan, where the United Kingdom is the second-largest contributor of foreign troops, after the United States.

Cameron's government, which came to power in May, announced the reductions a day ahead of revealing how it plans to cut spending across the board in the face of deficits.

"Defense cannot continue on unaffordable footing," the government said in a statement explaining the Strategic Defense and Security Review, as the exercise was called.

"Tough decisions are required to reconfigure our armed forces to confront future threats whilst we also tackle the 38 billion pound (about $60 billion) deficit that has accumulated in the 12 years since the last Defense Review," Fox said.

The Army is set to drop from about 102,000 to 95,000 personnel by 2015. The Navy will fall from 35,000 to 30,000, and the Air Force from 38,000 to 33,000.

The United Kingdom intends to be able to field a brigade of up to 30,000 troops for overseas deployments, the ministry said.