The UKVI have published updated advice which includes guidance for those who cannot leave the UK by Aug 31 and whose leave to remain has expired or will do so on 31 August.

 

The relevent section reads:

If you intend to leave the UK but are not able to do so by 31 August 2020, you may request additional time to stay, also known as ‘exceptional assurance’, by contacting the coronavirus immigration team (CIT).

The grant of an assurance does not grant you leave but will act as a short-term protection against any adverse action or consequences after your leave has expired.

After you’ve completed the form, you’ll be told what you’ll need to submit to show you can’t leave the UK.

 

Covid-19 advice for UK visa applicants and temporary UK residents

Something I posted on another thread. 

I should also add Thais and foreigners can register for a repat flight but the 3 August flights are full. The September flights will not be advertised until he end of the month. Demand has far out stripped supply as only 5 business class and 255 economy seats are available. No social distancing on the flights. On an interesting aside TAT have restarted their Amazing Thailand adverts and its new adverts which are much better than the tired old ones of previous campaigns.