Ages ago, during a comments thread discussion here about British nuclear weapons and Trident replacement, Chris Lightfoot (peace and blessings be upon him) suggested the option of "virtual" nuclear capability; that is, maintaining all the necessary technology, keeping the plans on the books, but not actually making a bomb. The canonical example is Japan, which could build one tomorrow but doesn't. But quite a few countries have such a policy or have had one. Germany is an example.
So, strangely enough, is Sweden, which maintained a major nuclear research program from 1945 to 1972 which was in many respects indistinguishable from actually making a bomb. Uranium supplies were identified, accelerators and reactors tested, bombs designed, and time-sharing arranged on French computers to check out the designs. The general staff carried out scenario-planning exercises to consider the strategy and tactics involved.
I quite like the idea - call it the Lightfoot plan - but there is a serious problem. Its main point is to get rid of teh bombs and save money, whilst getting around the problem that it's very difficult to reverse course if it turns out to be a bad decision. In a sense, the UK nuclear weapons programme has maintained these skills in existence artificially. Deciding not to keep going would make it very hard to keep them in being. Why? Well - even modern Sweden wouldn't find it that hard to build a bomb. They have nuclear power, and various engineering companies whose operations are suited to the job, such as Saab, Bofors, and (at least for electronics and systems integration) Ericsson. This goes double, or triple, for Germany or Japan.
Well, there's always BAE...but would you trust them with plutonium? For quite a range of the skills required, there's nowt in the UK beyond the civil service nuclear world to employ you.