There's nobody we'd ever launch them at that the Americans or Russians won't nuke first
Don't count on it. For a start Russia is, and will continue to be, the biggest threat to the U.K.; based on the tried and tested policy of our always confronting the Continental power seeking hegemony; and increasingly that will be Putin's Russia. So the idea that we'd look to Russia for protection is a bit suspect. And that leaves the USA. No offence to our 'cousins' but for the forseeable future the USA will be caught up the classic 'end of empire' fixation on a foe that does not warrant the effort currently being expended; and by default (of Blair's years of apalling leadership), has also dragged the U.K. into the same mess.
Britains decision to have an independent nuclear detterent came (in part) out of its experience in WWII of being bombed. As a small island vulnerable to attack by a foreign power from the air, it made sense to have a deterrent that made such an attack extremely risky to the perpetrator. As the world becomes increasingly destabilised, it would still make sense for the U.K. to maintain a deterrent. Personally, I would like to see the end of the need for nuclear weapons, but I beleive (for my country) that would be a foolish move at present.