I didn't realise that this spider was living under the lid of our water butt until I lifted the lid and the spider fell into the water. I thought it would need rescuing because, as you can see from the photo, most its legs had penetrated the surface film. But it was made of sterner stuff .....
.... and, resting its hairy waterproof body on the surface, it heaved its legs out of the water as if it was wading through treacle, lifting them high in the air, as with the left fore-leg in this picture, then ....
..... it rested each hair foot on the surface film and scooted across the water surface to the edge of the water butt and climbed out, none the worse for wear.
I guess it probably lived under the water butt lid because it liked the relatively warm, humid atmosphere - that large mass of water retains heat well into the night .......... and there are also plenty of prey items that crawl in under the rim of the lid.
I'll be a bit more careful next time I lift the lid.
Africa Gomez has very kindly identified the spider for me as a female Amaurobius similis.