Well I posted to the support newsgroup and got a few "we'll look into it" replies. But it's still happening. Intermittent, random, localised problems like this can be very hard to track down so it doesn't surprise me that VM support won't have the time to solve it.
Guess I might have to look for an alternate entry point to the Internet, as that's the simplest solution as far as I can see. Which is a shame, as I've had good service from Diamond Cable/NTL/Virgin Media over the years. But this problem plus traffic shaping plus dial-up speeds in the evening adds up to more irritation than I feel I have the right to be paying for.
