The Test to Release for International Travel scheme is for people who need to self-isolate on arrival in England.
Under the scheme you can choose to pay for a private COVID-19 test. The earliest you can take the test is 5 full days after you left a destination not on the
travel corridor list. If the result is negative, you can stop self-isolating.
The scheme is voluntary and applies to those self-isolating in England only.
The issue will always be that the scheme is voluntary. How many people will pay more for a test than in some cases a flight is debatable but I live in hope.