Proviris Solutions is Government approved to provide the Test to Release tests and certificates. If you want to end your mandatory 14-day self-isolation early, then you can pre-order the Test to Release for international travel test.
You cannot take a test to release test until you have been in England for 5 full days. You take a self-swab test at your accommodation using the test kits on or before day-2 and on or after day 8. If your day-2 test result is negative, you can be released from self-isolation. You will still need to take a test on or after day 8 to check that you do not have COVID-19.