Apparently we now need Trident to 'punch above our weight' .
http://www.bbc.co.uk/news/uk-35566480
So it's no longer for defence, it's a status and willy waving thing. The UK hasn't been a superpower for a long time now, time we got used to that, we're just another European country, who are best sticking with our neighbours for defence. No wonder the US are keen for us to retain it, purely for their own first line of defence reasons. They totally control it anyway, so it wouldn't be used in UK interests.
We really don't need it, if only for the obscene cost. Jeremy may be not to everyones taste, but he's right on this one.