I can read moron and I have three experiences of overstay and I used to travel in and out of Thailand tens of dozens of times unlike the touristy, I have retired there experts. By the way, how do you think I post replies if I can't read?
Well according to your post they told YOU your 30 days allowed in Thailand started in London @Heathrow. If that's not hilarious I don't know what is 🤔
I don't believe some of the ridiculous comments on this. Obviously by people who have no idea of overstaying and with regard to a comment, it's not worth risking a five year ban for a one day overstay, that is the most stupid comment I've ever read.
The 500,00 THB equivalent can be in your UK bank account, doesn't have to be in a Thai bank account. After one 180 day extension you have to leave/cross a border out of Thailand. Whether there is any stipulation as to whether you can leave and re-enter the same day is not known at the moment. What I'd do is go to the immigration office where you get your first 180 day extension and ask them whether you can re-enter the same day. It's Upto the IO., at the end of the day.