Clacket Lane appears to have all the requirements for being designated an emperor "hot-spot" - toilets, refreshments, easy parking and cover if the weather turns nasty!
For those out-of-towners I've attached a map - he's picked a great site readily accessible from the motorway network - just inside Surrey by a whisker from Kent. The interpretive centre is unfortunately on hold, as a result of Cameron's swingeing cuts, but plans are afoot to blockade the M25 with trucks, a la mode du fermier francais, if they're not rapidly reinstated.
So far, larvae only. Who'll be first to report adult iris from this prime location?