Just for reference:

Thailand has 20.6 new cases per million population per day.
The UK has 37 new cases per million population per day.
India has 211 new cases per million population per day. And has been added onto the UK red list for hotel quarantine on arrival to the UK.
France has 659 new cases per million population per day. Not on UK red list.

Figures taken from world meters & are just a snapshot, with no smoothing.

1 Thailand ought to be a long way from becoming a UK red list country at present. However, case rates are not the main factor. Pakistan was already on the red list, with 24 daily cases per million. The presence of variants and trust in the countries testing and genetic sequencing are factors. I suspect it's the "discovered in India" variant that's mainly responsible for India going on the red list.

2 The Thai daily rate is just over half the UK level. Of course, the UK is on a firm downtrend and the UK cases ought to do a lot less damage from now on, as all the high risk people have been offered at least one dose of the vaccine.