People are still avoiding answering my question, so I'll answer it myself. The OP asks:
*This idea has been mooted before. However it now is looks like it might begin to happen in a systematic way, due to the government keeping the NHS so desperately short of the money it needs if it is to maintain current levels of service.
It is more expensive and more difficult to operate on people who are overweight, and who smoke. They are likely to be in hospital longer. They are less likely to make a successful recovery and feel the benefits. Is this is sensible way to ration NHS surgical treatment?*
On the face of it, it sounds like a sensible idea to me. And if, as been mentioned by a poster or two in this thread, it happens already (docs advise, possibly even insist, that patients lose weight or stop smoking before it is worth scheduling certain surgical procedures or else the procedure is basically wasted on them), why was the question even asked?