Hi Piers and Alexander,
Delighted that you got to see the QoS! I actually included you Alexander in a group Email invitation last weekend, but the address I have for you is out-of-date I think (returned to sender). The 'publicity' issue is one that I considered very carefully. It's a difficult balancing act between giving as many people as possible the opportunity to see something like this, and starting a stampede that can be potentially damaging to either habitat or the chances of unhampered breeding (plenty of examples - such as the damage to habitat at Stockbridge Down). Initially I contacted medium sized groups of people directly, on a daily basis, so as to spread the load. It was then put out more widely, so that the number of visitors has never been problematic. The odd person disagrees with this approach, but that's just tough!
In the vast majority of cases I think that being 'open' is best, as a regular presence of enthusiasts is more likely to curtail inappropriate behaviour and even collecting. However, there will always be the odd case where secrecy has to be maintained (e.g. conservation of rarities on private land, where publicity and subsequent trespass may lead to the right to perform that work being withdrawn by the landowner). As it is, these butterflies are giving a lot of people an awful lot of pleasure - which is how it should be!
As far as I can determine there are two QoS still alive, and both should last the weekend with ease. With regard to the comments above - if you see the male, sunbathing on the path or beating up Clouded Yellows, it doesn't harm to stick your lens in his face (he's very user-friendly). However, there is a very fresh condition female around, carrying a valuable cargo of eggs. So if you see a QoS fluttering amongst the maize stalks on the margin of the field, please give her some space. She was mated on Monday, providing a sight I never thought I would EVER see in the UK. A few of us had been watching the male with the spots joined to form a dumbell shape (last few pics) when I spotted a very fresh looking female, who turned out to be a virgin. She flew over his territory and after the briefest of tumbles they paired for 25 minutes (photos taken from range with 'zoom'). Magical! She then retired to roost 60' up in a sweet chestnut.
To anyone visiting this weekend - happy hunting!
Neil
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Thanks for the Q of S info Kipper. At least 8, probably more, Clouded yellows on Bullers Cliff hill, near Abbotsbury beach today. Unfortunately, i couldn't get near the blighters for photography. 
