IF the UK wishes to have a deterrent then it has to stay in the submarine business. In the event of a serious war they'll be the main forces available.
It's expensive but a lot of the money is spent within the UK
The "Astutes" have their problems but seem generally to be rated of equivalent quality (but different from in detailed capabilities) to the USN "Virginia's" - in other words some of the best around. There isn't any other UK military asset you can say that about - maybe throw in GCHQ.
The real question will be can they gradually ramp up capability to shorten delivery times?