Britain has signed a 350 million pound contract to upgrade one of its nuclear submarines in a move that the Ministry of Defence on Monday said would secure 2,000 jobs.

Under the contract, worth 420 million euros ($555 million), workers at Babcock's Devonport Dockyard in southwest England will install the Royal Navy's HMS Vanguard with a new reactor core and carry out a refit and refuel.

Defence Secretary Phillip Hammond was set to confirm the deal during a visit to Devonport on Monday.

He was expected to say the contract would secure more than a thousand jobs at the site, 300 more at other companies in the city and 700 jobs in the industrial supply chain across Britain.

"As well as securing 2,000 UK jobs, this contract will ensure the nuclear deterrent submarine fleet can continue to operate safely and effectively to maintain a continuous at sea deterrent," Hammond will say, according to extracts of his speech released by his office.

HMS Vengeance is one of the UK's four Vanguard-class submarines designed to carry Trident nuclear missiles.

The upgrade is scheduled to take three and a half years.