Whilst it is frowned upon unless in the right situation, SAR UK winchmen do come off the wire, pretty frequently. Yes only when its safe, but thats their call to do so. Generally most mountain ops in Wales or Scotland, and most boat jobs. In addition, cave jobs (Devon).
Come off the wire and go diving (using the 'stass') will get you a talking to..(Harbour in Wales).
Crab is correct in saying 90% of the time the winchman is deployed direct to the casualty, I might add the other 10% of the time the winchman will adapt the situation to achieve a result and its probably less than 0.1% of the time that it can't be achieved.
I am a firm believer that equipement should not be withheld because it may be only needed Once, and a sixteen man basket should, for all the minimal cost involved probably be kept at each SAR station in the UK.
A conventional basket ala US is really no more than the double strop lift developed to reduce the impact of lifing a person submerged in the water, which arose from the Fastnet race in 1979. The double strop placement does not require the winchmen to come off the hook, and allows the cas to be lifted semi-recumbent.
All in all the present UK system is pretty good, not with standing it needs some decent (sic) pilots to hover the a/c!