We don't need a nuclear deterrent, we just need to cut all ties with the United States of America, and stop playing their lapdog. The USA however supplies us with nothing of any value, and simply wishes to annex the UK as the 51st state. This is really why Scotland and Wales want their independence.
Since Russia have all the Gas, we need closer ties with them in order to keep our houses heated and the lights on. We also need closer ties with European, African and Middle Eastern nations who supply the UK with everything we need.
The only nation to use a nuclear/atomic bomb in anger is the USA, so if we did need any form of deterrent it would be to stop them, and not our friends from the near, middle and far east.