Can anyone enlighten me on how wind is measured in the sim? When the tower tells me surface wind is 158 at 122, I'm thinking I oughtn't be able to get the door closed after a weather check, let alone think about walking across the airfield to a plane that has surely blown away.

Even aloft, these are incredible speeds. Is this a bug, or am I reading something wrong?

Well, 100 knots bearing 230 degrees at height is perfectly possible, yes. Gets windy up there!

I think he was talking about Surface Wind!

Yes, my main concern was surface speed, since it was immediately obvious that the wind wasn't really blowing that fast. At the time I received 158 @ 122 for surface wind, the tower also reported 061 @ 122 for winds aloft (which is why I mentioned aloft speeds as well, but I didn't make that clear). Typically, the wind speeds are very small values, which leads me to believe this is some sort of bug that erroneously populates the speed value in the tower report with "122".

Also, from what I understand, the prevailing wind in southern Britain is west-to-east, and Bader's post seems to verify that. I seem to recall someone mentioning the wind blowing "backwards" in a post awhile back. Maybe that's what this is.

It seems there may be two things wrong then:
1. Erroneously reported wind speeds of 122
2. Wind blowing the wrong way at altitude.

I mentioned this quite a while back, the prevailing wind in the U.K is normally from the west to the east. Surface winds at coastal airfields could quite correctly south to north or east to west to allow for local conditions such on or off shore breezes but not very likely at inland airfields.
The winds aloft sound extremley fanciful. I've been flying for nearly 30 years (airline, heavy metal) and believe me a wind at 25000ft of 50 knots is heading towards jetstream conditions a more normal wind speed at 25000-30000ft would be in the region of 20 to 35 knots.