I would be surprised if the UK removes Thailand from the red list after having just put Thailand on the red list. Its more likely that Thailand will remain on the red list for some time. Dubai remained on the red list for 7 months (UAE) and those middle eastern countries have plenty of money to spend on vaccines. I was surprised that Thailand went on the red list but maybe they don't want Brits coming to Thailand on holiday, getting covid, and then returning with a new varient?