Definitely best not to risk it. Just pointing out that it’s 100% complaint to leave the day it expires and that if overstaying for 1 day, the result should be a 500 baht fine.
That's why I said "if you need to" – it's supposed to be a last resort. I've done it over 10 times and had no issues. My friends and family have done it lots too. Up to you OP!
Also if you need to, you can extend your exemption stamp for another 7 days (1900 THB again) at the Koh Tao immigration office. Let them know you’ve got a border trip arranged for a few days later and they should approve.
How long will you stay in Thailand? You don’t need a visa with a UK passport. You get a stamp on arrival for 30 days and can extend it for another 30 days for 1,900 baht once in Thailand, then you can extend it for another 60 days for another 1,900 baht, and despite what people say, this is seemingly going on for a very long time. It’s been going on since I arrived in April 2021.