I am pretty sure, that it is a Chinese mini drone.
In the last couple of years we had more and more in Germany observing garages, sheds and artisan working spaces, to spy out our ingenious working systems.
They even observed simple house wives to get out how to cook well tasting meals!
I think, because they are unable to copy us, they now started to observe British sheds and kitchens because they probably think, that your technical level would be lower.
Should they start next time to have bacon and eggs for breakfast and fish and chips for dinner, you will know why!