The US has already planed to extend the Ohio Class Trident SSBN lifespan from 30 to 42 years. The UK could be taking the US lead and may extend it's Vanguard Class Trident SSBN to a similar length.
From The Herald in the UK "Trident fleet faces stretched lifespan to help curb defence costs"
(Hat tip: NOSI - Naval Open Source Intelligence)
BRITAIN is to try to stretch the operational lifespan of its four Trident missile submarines until at least 2035 to maintain its nuclear deterrent at minimal cost and risk, according to naval sources.
Tony Blair and John Reid, defence secretary, have both insisted recently that no decisions have been taken, but sources say they have already scrapped alternative plans for aircraft or submarine-launched cruise missiles tipped with nuclear warheads.
They have also rejected building a new generation of submarines despite the fact that replacing ageing intercontinental missiles, installing new reactor cores, and redesigning the existing British warheads could cost more than the original £12.2bn paid for the Trident system in the 1990s.
Royal Navy Vanguard SSBN
The lead UK boat is the HMS Vanguard commissioned in 1993. If the lifespan of this class is extended to 2035 this would put it in the same timeframe for replacement as the US Tridents. The last US Trident commissioned was the USS Louisiana SSBN 743 on 9/06/1997.
As of this date, there is no large-scale design or production program in place by either country to replace thier Trident Submarines. The development of a SSBN-X Follow-on to the Trident should start in the next 10 years. This is in order to replace the first of the Tridents to be decommissioned in approximately 2029.