In reply to dagibbs:
> Currently on the list is some classic grit stone, probably Stanage.
In summer? Ugh. I suppose if you will only climb in the UK once then you have to do this, but gritstone is not at its best in summer - midges, poor friction - and the moderate stuff Stanage is (so I hear) polished & crowded these days. This would be something like going on a once in a lifetime trip climbing trip to the USA an choosing the Gunks over Yosemite.
(UKC gritstone fiends will howl at me now)
Depending on how experienced & confident you and your friends are at multipitch stuff and dealing with slightly awkward approaches & a bit of commitment, the other UK Climbing Thing besides gritstone that you absolutely must experience is sea cliff climbing. I gather there's a lot a relatively approachable stuff in North Pembroke, although I only went there once a long time ago.
Depending on how far you're pushing the boat out at HVS, the definitive photogenic ultra-classic sea cliff HVS to push the boat out on is A Dream Of White Horses at Gogarth. But really not a route you'd want to get into trouble on (which of course is part of its classicness)
Otherwise, and especially if you're ok on multipitch, in summer I would go for mountain routes in North Wales, the Lake District or Scotland over the Peak District every time. Torridon, on the NW coast of mainland Scotland, is one of the most beautiful places on earth and has fantastic climbing.
Moderate grade sport climbing in the UK tends to be deeply mediocre and, for a visitor, is only worth considering if a sport crag happens to be the only dry rock near where you are at the time. Which can happen: having a limited choice of nearby dry rock is also a prominent feature of British climbing. I assume you already knew that?