even the nettles are wilting
Really feel for you in the SE, it's about 5 degrees cooler here but still pretty roasting. Last week we noticed bracken on Dartmoor wilting, never seen that before.
Wet towels are a great idea, and a fan behind a wet towel over a chair even better. I saw a suggestion for freezing bottles of water and standing them in a dish in front of the fan, sort of DIY air conditioning.
One garden game we've been playing is bobbing for iceblocks; I freeze water in plastic yoghurt pots, fill up a trug with water and drop the ice in for Kipper to fish out. He tends to drop it straight back in and it melts pretty quickly, but it's quite entertaining and cooling, and he tends to drink a fair bit in the process. He's also learning to blow bubbles through his nose which is funny!