We no longer can afford an SSBN based nuclear deterrent. The error was made many years ago when we became reliant on US missile and targeting technology. A pan European approach with France would have been the better option. Corbyn is a realist. The UK will shortly lose many friends as BREXIT will have impacts far beyond the EU, Trumps America first policy means the "special relationship" is dead. Trump will go the way which serves the US best. And who can blame him for that.
We need to spend the cash on increased conventional forces instead. A blue water navy of Frigates and Destroyers. SSNs equipped with cruise missiles. why not a nuclear tipped Tomahawk or similar. Not a global reach weapon but flexible and threat multiplied.by the number of platforms.