In reply to Otis:
Cheers for your comments everyone. Having looked back through the HVD's I have done, there are certainly one or two in there that caused me to raise an eyebrow at the time due to being 'interesting' (the top out on Karabiner Chimney was a giggle - afterwards!)
Looking at the BMC grade comparison table, plus the grade table in my A55 sport climb guide book, it's interesting to note that HVD as a grade is completely absent, with VDiff running straight into Severe.
I think that where the HVD grade exists in an area I climb in (e.g. west side of the peak district) I'll take note of it and pick routes accordingly. However, where it clearly isn't in favaour (such as N Wales) it's just time to acknowledge that the next step up from VDiff is Severe and not to get too hung up on grades when I want to push on a bit!
Mike.