Hans Kristensen and Matt Korda have published their latest analyses of the US and Russian nuclear arsenals. Perhaps the best publicly available and readily accessible information on the topic.
The UK's "Integrated Review of Security, Defence, Development and Foreign Policy" has just been published. Of particular interest to me is a reversal of the previous policy of gradual reduction of nuclear weapons down to 180 warheads. There will now be a gradual increase, with a new ceiling of 260 warheads (pp. 76-78). The strategy surrounding these weapons is marked, in part, by an official emphasis on "deliberate ambiguity".
All this is, of course, accompanied by a ritualistic, politically necessary and perhaps laughable affirmation of the goal of "a world without nuclear weapons" and "full implementation of the NPT in all its aspects, including nuclear disarmament..."
Hans Kristensen has published a critical commentary. For a more pro-nuclear opinion piece which looks at aspects of the US-UK nuclear relationship, see Linton Brooks et al.
For a sense of just how speculative some of the commentary has been, see the article by Mathew Harries in the Bulletin of the Atomic Scientists. As Harries notes, we just don't know what, exactly, is behind the UK adjustment to nuclear weapons policy.