Thanks Huw - I though the actual message Virgin comes up with would help and thought I'd cropped the pic sufficiently. It is rather frustrating as I'm now 14 hours into my working day and would really like this problem sorted.
It isn't much of a one-off. Dozens of people and organizations have been reporting problems for months with the poorly-tuned spam checking which is preventing them from delivering legitimate emails to Virgin Media accounts. You can read some of the many reports here: