I wondered whether someone will try the M25 with the current quiet roads. Remember in 2018 in the guy who did lands end to john o'groats in 9hrs 36mins in a Audi S5 averaging over 90mph. I recon the M25 could easily be done in 56 mins averaging 122mph. Not quite sure how you'd manage to get past all the cameras though!
Having said that, it would take a bloody good driver to manage such a high average speed for so long on public roads!