Actually finding concrete numbers on numerous aspects of WW2 can be quite difficult, as there is often someone willing to challenge the accuracy of any figures quoted.
From a very old WW2 'fact book' still on my bookshelves, there are totals of of 144,079 killed, 239,575 wounded and 152,076 PoW for the British Army during the conflict. The same book states 70,253 RAF personnel as killed or missing (but does not give figures for PoW). There is no entry for the RN unforunately. An online source gives 63,787 -http://www.naval-history.net/xDKCas1003-Intro.htm#table
Another equally old book, a WW2 Chronology, gives British military casualties as 264,443 killed or died or wounds, 277,077 wounded and 213,919 captured or missing. Civilian deaths are shown as 92,673 (of which some 30,248 where Merchant Navy). Getting those figures to tally with others quoted in this relatively short thread is exceedingly difficult.
I agree it should be fairly straightforward to obtain reliable figures, but there are numerous complications. How many missing turned out to be killed in action or captivity, and how many were returned home is an obvious one. Accurate record keeping in the midst of war is another challenge. Lots of war diaries were lost, and with them details of the fates of men. Also the figures compiled run on postwar as men succumbed to wounds received some time earlier. On the basic point of combat versus accidental deaths or disease, I'm not sure there was such attention paid to each circumstance then as there would be now. I'd also bet there'd be conflicting figures for more recent and shorter wars.
For a brief idea of the complexity, just look at one review of Bomber Command casualties, not RAF overall - http://www.rafinfo.org.uk/BCWW2Losses/B ... sstats.htm