British defence group BAE Systems on Monday said it had won a second contract from the government to design Britain's next generation of nuclear submarines.

BAE and the government said the contract was worth �315 million ($505 million, 391 million euros). The company had already won an initial design contract worth �328 million in May regarding the same project.

The Ministry of Defence confirmed the new deal in a separate statement, adding that British engineering support services Babcock had been awarded a submarine design contract worth �38 million.

"This further work underlines the MoD's confidence in our ability to deliver a design that will meet the future needs of the nations nuclear deterrent," BAE said.

The new class of submarines were to replace the current Vanguard fleet carrying Trident nuclear missiles, although the final decision on replacements and their numbers would not be taken before 2016.

Britain has four Vanguard-class subs which are expected to be decommissioned in the late 2020s, though their missiles should remain operational until 2042.