In the UK, experiences vary. The new Caledonian Sleeper (London-Highlands) is apparently a pretty rubbish experience. However, I took the Night Riviera (London - Cornwall) a few years ago and found it a pretty good experience even though I very nearly missed my stop in Truro. The problem for a business traveller is that you would need a shower.
The other problem facing the Caledonian sleeper is that London-Glasgow is only something like 4 hours and the day trains are very good. The same is not so true for getting out to Cornwall.