Peter - sorry I haven't got back to you before but this retirement malarkey is taking up a lot of time! Your caterpillar certainly appears to be a Peppered Moth. Your description fits it perfectly and it also the right time of year : Oak and Pale Oak Beauty caterpillars have usually pupated by August at the latest. The reason it appeared sickly could be that it had been nobbled by a parasitic wasp; alternatively, it could have been making its way to the ground in order to pupate. The caterpillar featured here, a Pale Tussock, is a lot easier to identify! It's colours are indicative of a foul taste - I must admit that if I was a bird I wouldn't fancy it much! It turned up during a fungi foray at Epping. Another find recently was this Minotour Beetle at The Backwarden EWT Reserve, Danbury, also during a foray. Apparently it buries rabbit droppings, on which its larvae feed.
