Because we've had a lot of talk about tests recently a couple of observations.
With infection rates high, the odds of a LFT giving a false positive are lower than the odds of a PCR test giving a false negative. If the LFT says you're infected and the PCR says you aren't, you need to be suspicious - at least do another LFT test to make sure.
A PCR done one morning can be too early to pick up an infection that's visible on LFT the next day. A negative PCR done two days ago is basically useless today. PCRs can see a lower viral load, which means they can pick up an infection maybe a day earlier than a LFT and they may continue to give a positive result for days (or weeks) after the LFT goes back to seeing negatives again - in general though those late PCR positives are seeing dead viral material not the infectious kind. The early PCR positives are obviously useful though, and PCRs can pick up asymptomatic cases that LFTS miss - provided you get the timing right.
The FT did a graphic based on the data: