What targets does the UK envisage for their multi-million pound nuclear missiles?

There is one reason we have nukes and one alone; America.

Since WW2 and Britain 'lost' its empire, our political establishment have decided that the only way to have a 'presence' in the world is to try really painfully hard to be BFF with America. Hence all our politicians talk of the 'special relationship,' which no American I have ever met has even heard of.

Joining NATO, buying American nukes, partaking in their wars, working with the NSA... it all fits the same pattern. In military, diplomatic and intelligence terms, the UK is pretty much a US satellite country; even now, long after the cold war. All the talk of British interests and national security is pretty much really about that.

The British Ruling class is an extension of the American establishment and I say that as a Brit. The answer to your question is 'nobody'.