We have a very capable anti ballistic system that could take down any nuke heading our way, as do france, the US, Russia etc, so even if one was fired by any side they would probably be shot down, if mutiple were fired it wouldn't matter if we could fire one back we would all be dead anyway, so spunking 250 billion plus on something we will never use, when a more modern upgrade of our navy and airforce would be money better spent, and use barrow shipyards to build the new navy so jobs are sucure
In the future any nuke will be deployed by drones more than likely, so keep a nuclear deterant, but one suited to modern warfare not the cold war.
We have already developed one of the best missile systems in brimstone recently, that can be adapted for duel use, trident isn't necessary or affordable, just posturing for the sake of it. I would rather have a more technically advanced army/navy/RAF with a modern nuclear final option.