Well, apologies to my ma for posting again on "creepy crawlies", but these two flies were blissfully engaged in a spot of Sawfly lurve on the underneath of one of our Jerusalem (f)artichoke leaves. I couldn't resist taking a couple of photos, just to, er... capture the romance of it all.
NB. 21/09/07 I am now pretty convinced these are large Rose Sawflies - Arge Panana. They normally feed on nectar but also feed on leaves also, and not just next doors' Rose bush!
I've altered the title of the post to reflect this identification.