Having just gone through LHR on an overnight transit, I can now clarify the procedure based on my own experience. When you complete the UK passenger locator form online, it’s very clear that a landside transit, including overnight transit (within 24 hours), does not require either quarantine or day 2/8 testing. Following the guidance in the form, you select “stay in UK” then go to the list of exemptions for the post-arrival testing. Those exemptions are almost all job-based, but various categories of landside transit passengers can also be found right there in the alphabetical list of exemptions in the locator form, under “transit,” and, even more specifically (in our case), there’s a choice for landside transit in England, departing from England.

You still need to do a COVID test for the incoming flight into LHR; an antigen test is fine, and we used the monitored BinaxNOW/eMed antigen test, which is intended specifically for return to the US but also meets the UK testing criteria.

Upon arrival, the border officer was very clear about the regulations, checked our incoming COVID test results, had a look at our PLF, and sent us on our way.

After having waded through all the conflicting and contradictory information on here, it was all very straightforward in the end, and I’m glad we didn’t just chuck a few hundred extra pounds or dollars out the window pre-paying for tests that we would never have been around to take.

My only other note is that the arrivals hall at T5 was pretty crowded—nothing like the 5-10 minute experiences I’d been reading about on here. It took us a good 40-50 minutes to get through; the e-gates were mostly out of service and weren’t any faster than the regular border booths.