hulahoop7
Not a Boffin notes one drawback of TLAM in the role you depict; there are many other technical and military problems with both the weapon and platform in the role you suggest. That is not to say that it is totally unfeasible; after all the basic concept is similar. My instinct tells me that to overcome all the shortcomings you'd end up with a capability well short of Trident, without the same relative decrease in cost.
However, stick a pin in that and for the sake of argument, say that it could be made technologically possible and yield a decent cost saving. It might just create a far bigger problem.
The UK's nuclear posture is locked into strategy and policy developed in the 1960's because we are one of five priviledged states under the Nuclear Non-Proliferation Treaty (NPT). the others being China, Russia, France and the US. This Treaty is accepted as discrimantory by its signatories (most, but not all, of the world's sovereign states) on the grounds that it remains the best hope for non-proliferation. On those grounds the big five are expected to play the game by everybody else - and bear in mind it is a treaty largely based on goodwill, rather than legal enforcement.
If the UK's argument for being one of the five legal nuclear powers states that it is part of the balance necessary for global nuclear peace, significantly altering our posture/policy/capability leaves other states to once again raise the question why not us? A low capability nuclear option would be a very attractive package for many countries around the globe, including a number that have all the technology they need right in place (Japan for example). Indeed this very point was made recently by the US representative on Non Proliferation.
History shows us that once a state drops out the NPT (or never signed up to it) it can go nuclear in short order - Israel, India, Pakistan and North Korea.
Add all that up and I think many countries would be of the view that either we replace Trident like for like, or we step back and unilaterally disarm our nuclear capability. Which by the way is the long term goal of the NPT.