The short answer? No, it’s not illegal! You can stop reading here if you came to prove a point to someone, but there is a catch.
Technically, there’s no UK law that states you must wear specific shoes, or any at all, while driving, so you’re not going to get fined or be given points on your license for wearing the footwear of your choice. However, Rule 97 of the Highway Code advises that your footwear shouldn’t prevent you from using the controls correctly, so if you drive in a way that puts others at risk, whether that’s because your barefoot, in flip-flops, or wearing unsuitable shoes, you could be charged with careless or dangerous driving.
So, while the law doesn’t specifically ban barefoot driving, you could still face legal consequences if your choice of footwear is inappropriate and affects your driving ability.