https://covid19-waiting-time.thejoin.tech/ Obviously it’s only as good as the latest update, but may be helpful in deciding what time to head out. You just need to set the location, and then click on the supermarket of choice.
Slight tangent. Saw a bloke coming out of Asda last night carrying a 3ft garden gnome under his arm. Sorry, I realise this sounds like it needs a punchline, but it's a true story. He hadn't bought anything else, just the garden gnome. Made me think of Basil Fawlty.