Got in One!!
Why waste a few £bn getting a system that would possibly be out of date in the late 80's, early 90's when they can spend the same amount procuring Trident C1 which was then upgraded further before purchasing Trident D.II.
Don't forget, although the renting of the missiles (minus the front end "bus") was easy, could it be that it was more cost effective to build a completely new class of SSBN's to hold Trident than to refit the aging RESOLUTION class rto take Posiedon for a limited length of service.
Designing and building the SSBN fleet is the most costly part of the UK's deterrent.
Regards filers
The timing isn't right for that to be the case, Super Antelope was thought of even before all Resolution boats were delivered, the initial study was undertaken in 1971 and the procurement decision taken in 1975. Trident wasn't one of the options put forward in the early 70s, in fact the Admiralty wanted the then new Poseidon.
I think the reason Trident gets bought up is because of the time delays with Chevaline, I doubt that in 1975 the people involved thought the system wouldn't be in service until 1982.
As it happens the more I learn about it the more I think Chevaline was the right thing to do from a whole of Government perspective. I shudder to think of what it would have cost for Britain to develop a new front end and build hundreds of new warheads for Poseidon, assuming they had the physical capacity to do so.