International services firm Serco is to retain its contract to manage and operate the UK Atomic Weapons Establishment - the arm of the military which builds and maintains Britain's nuclear warheads.Serco has had the contract since 2000 - it is worth around £300m per year and the extension will run between 2013 and 2018, adding £1.5bn to the firm's order book.The work is done in tandem with Lockheed Martin and Jacobs Engineering Group.Christopher Hyman, Chief Executive of Serco, said: "We are delighted to have successfully agreed this latest pricing period for our AWE contract. "Working closely with the Ministry of Defence and our joint venture partners, we are delivering a critical component of national security and providing leading scientific research as well as delivering value for money for the taxpayer," he said.BS