I was pointed (by this forum) to this site for tyres and complete wheels. Just bought 2 tyres recently, no probs turning up and getting them fitted. Saved £80 by not getting them at a large tyre fitter. https://www.tyres-pneus-online.co.uk
Incidentally, these tyres were "seal inside" tyres. A third option instead of gunk/goop or a spare. No use with blow outs (but recovery will help there), but even relatively large punctures in the main tread are sealed instantly without needing to stop, or reduce your speed. The "repair" requires the scraping back of the seal layer (stuck on the inside on the tyre), inserting plug, and replacing the seal over the top. Seems to work well. Has saved me having to rescue the wife a number of times.