Trident and previous weapons of that ilk are political devices, and should be considered seperately from the mundane stuff that goes thud, bang and whizz... the government should fund it seperately IF they wish to retain the capability, as it's the politicians who will decide if and when to employ it.
Then give the armed forces the cash they need to do the job they are told to do with conventional weapons. I don't really give a hoot about SSBNs, simply because our conventional forces are becoming so tiny that nobody would need to go nuclear to push us aside anyhow...when your response is limited to nuking the opposition or doing nothing you've lost anyway.