March 26 (Reuters) - British defence services group Babcock International Group has been awarded a 350 million pound contract to upgrade a Royal Navy nuclear deterrent submarine, Defence Secretary Philip Hammond said on Monday. The deal to refit and refuel HMS Vengeance, of Britain's four nuclear-armed submarines, will sustain 1,000 jobs at Babcock in Plymouth, south west England, as well as a further 1,000 jobs in the supply chain, Hammond said. The upgrade is expected to take three a