The future of Oxfordshire military bases has been safeguarded by the Government's investment in defence over the next decade.

In the Strategic Defence and Security Review Prime Minister David Cameron has set out plans to spend £178 billion on buying and maintaining military equipment over the next decade.

But the new national security strategy also included big cuts to the Ministry of Defence's civilian workforce, which is set to be slashed by almost 30 per cent to 41,000 over the next five years.

The MoD now estimates that acquiring four new submarines to carry the Trident deterrent will cost £31 billion over the course of the 20-year procurement programme - compared to a previous estimate of £25 billion.

And a further £10 billion "contingency" has been set aside to meet additional unexpected cost increases, reflecting the complexity of the project, with the first submarine due to enter service in the early 2030s, the SDSR said.

The SDSR set out heavily-trailed plans for two new Army 5,000-strong "strike brigades" capable of deploying rapidly around the world, as well as an additional £12 billion of equipment funding.

They will form part of a joint maritime, land and air expeditionary force totalling 50,000 by 2025, compared to the current commitment of 30,000.

Up to 10,000 troops will also be made available for swift deployment to support the police in dealing with terror attacks of the kind seen earlier this month in Paris.

In other measures, the MoD will acquire nine Boeing P8 maritime patrol aircraft to plug the gap left by the highly-criticised decision in the last review in 2010 to scrap a new generation of Nimrod aircraft.

There will be a 10-year extension to the operational lifespan of the RAF's Typhoon jets and upgrade work to give them ground attack capabilities - effectively adding two additional frontline squadrons.

The Typhoons - fitted with upgraded stealth radar equipment - will now see service through to 2040 to answer RAF fears over the dwindling size of its resources.

The extended lifespan means there will be seven squadrons of around 12 aircraft.

The SAS and other special forces will get an extra £2 billion to improve their equipment, the RAF will double its number of drones, including unmanned craft which can "fly at the very edge of the earth's atmosphere and allow us to observe our adversaries for weeks on end".

And an extra £1.9 billion will be spent on cyber security and 1,900 new personnel recruited to the intelligence agencies.

Meanwhile, a separate strategy for official development assistance set out plans to use the UK's aid budget to help bolster security, including by focusing half of the Department for International Development's budget on support for fragile and broken states.

The strategy included an increase to £1.3 billion for the Government's Conflict, Stability and Security Fund, as well as creating a £1.3 billion fund to drive global prosperity and good governance, investing £1.5 billion in scientific research into global problems like anti-microbial resistance, and £1 billion for work to counter infectious diseases.

In a statement to the House of Commons, Mr Cameron said the Government had taken "a clear decision to invest in our security and safeguard our prosperity".

The Prime Minister said: "Our Armed Forces, police and security and intelligence services are the pride of our country.

"They are the finest in the world, and this Government will ensure they stay that way.

"Using our renewed economic strength, we will help them keep us safe for generations to come."