I agree Jacko.. I think we're being walked into Trident 2 without considering other cheaper, more appropriate options.
Why not build 3 extra Astutes - we need to keep them building to keep Barrow alive. Each Astute has the ability to carry 38 weapons (TLAM / Torps). Ensure that each one carries 8 nuclear tipped TLAMs + 15 standard TLAMs and 15 torps. In the event of a crisis, any at sea SSNs would be ordered to fire all TLAMs aboard, that's nuclear and non nuclear. If we take the 1 in 3 rule, that would mean 3 SNNs worth. That's a total of 69 TLAMS heading in on the enemy. 24 of which are nuclear tipped. I can't believe that it is beyond science and technology to arrange for all these missiles to be in the air at the same time.
Another option would be for one Astute to be designated the bomber - it could carry 30 nuclear TLAMS with 8 torps.
Many argue that the new generations of AAW systems degrade this style detterent and are becoming increasing available to none top tier states. But I'd counter that you'd have to be very brave to chap to chance those odds - particularly if only high yield warheads were used on each missile. I'd also argue, that if the UK were really going toe to toe with a state that could definitely knock out all of those 69 TLAMs, the world would be in such a sh8#t storm, everyone would be chucking N bombs around.
In addition, TLAM development isn't standng still. The US needs to be able to use them in a conventional strike too - so they are going to get better at penetrating AAW protected air space.