The UK’s Trident missiles are provided from a shared pool at the US Navy's Strategic Weapons Facility at Kings Bay, Georgia. The US undertakes maintenance of the missiles while they are pooled, at which time they are not allocated to either nation.
Under the Polaris Sales Agreement (amended for Trident) the UK pays the US Department of Defense an annual contribution towards the overall cost of the Strategic Weapons Facility. This contribution, which includes maintenance work, is based on the UK's share of the overall missile inventory, and historically has amounted to around £12 million a year.
There is no separate missile refurbishment program. However, in order to minimise the risk of obsolescence, the US is undertaking the Trident Life Extension program. MOD expenditure for this program (at outturn prices) for the last three years is:
We do not comment on operational matters for the purpose of safeguarding national security.