In the end I cracked, and gardened in the rain. I got soggy, and I got muddy, but all the plants were down or potted on or Chelsea snapped (my garden's a bit dense for chopping, so I tend to just snap off half the stems - any flowers or buds taken out by accident go into my garden vase). While I was digging holes for New Guinea Busy Lizzies and a colossal Borage (my third attempt to grow one -- one went to slugs, one was outcompeted by a geranium) I found that some elements of my spring top-dressing of home-made compost had not been dragged underground by the worms:
Yes, absolutely, those are tea bags. Tea bags, the mainstay of any British compost bin. But not just any teabag, no. These are luxury pyramid teabags. They feel slightly silky to the touch, they came filled with premium large leaf tea, and foolishly I thought that they would be biodegradable. Not so. They see to be about as biodegradable as a pair of tights, and are now officially a menace to the compost bin.