JTO - indeed, I couldn't have said it better.
WEBF: The Guardian piece is certainly accurate in one respect - there is very little clarity in the public domain over what the costs will be for:
(i) decommissioning the existing Trident infrastructure;
(ii) what the Trident-specific infrastructure is (eg, would we need to retain Vulcan and RR nuclear expertise for SSNs?);
(iii) how much the fully absorbed running costs for Trident are (ie, the V-boats, the Trident specific infrastructure, Trident's share of the shared infrastructure - eg Faslane, the AWE costs);
(iv) what the planned spending profile for the successor programme is;
(v) close down costs at Barrow if successor is cancelled.
It's a bit glib to say that "it's unlikely to save any cash immediately" as (i) and (v) will come due at some point - just not now. And the £100bn or so through-life cost of Trident has not been disputed by MoD, they simply prefer to talk about the £15 - £20bn capital cost of successor, which is like comparing the cost of growing grapes with the cost of buying champange.
So (given that this a rumour network) I Don't Know what the actual savings would be in the near term from (a) abandoning successor & Trident replacement and (b) from scrapping the V-Boats now and going down a different nuclear - or indeed, non-nuclear - road.
However, it is clear that over the next 30 years, binning Trident would save approximately £100bn.
S41