So the" Test to Release" is official https://www.gov.uk/government/news/t...ional-arrivals

I'm arriving back on the 8th December so interested to see if a) I can opt in to test either on the 15th or the 20th/21st and cut short my quarantine a little or b) if there will be any time benefit to leaving the UK for an overnight trip on the 14th Dec (depends on the testing turnaround)

Edit: just spotted "Passengers will be able to book a test from a provider on a GOV.UKlist before arriving in England. If they choose to book a test, they will need to state this on their passenger locator form prior to arriving and then go straight into self-isolation at home as usual. If they choose to opt in after arrival, they will need to resubmit their passenger locator form."

So I suspect I'll be out of luck (unless I travel out and back in again on the 15th but by the time I've tested I'd gain a day maybe for £100s!) but will be interesting to see if one can re-submit my form on the 15th and opt-in, will be of benefit to those arriving in the days before