What "mountains" were these? There are no mountains in the UK.
Nobody reads sigmets or airmets anyway so nothing unusual there.
But if wind flows over terrain then yes it can get bumpy. This is a good flyer on the subject:
http://www.caa.govt.nz/fulltext/Safe...n%20Flying.pdf
There isn't too much of a problem with -1000fpm VS because the air isn't going to flow
into the ground, so when you have descended to a few hundred feet, the downdraught should stop.