Not very, is my answer. Let me tell you why.
My daughter and I were about to set off on a long-planned journey to visit relatives 300 miles away in Cumbria. Just as we were leaving the house she received a phone call from her boss to tell her that one of her work colleagues had tested positive for Covid-19. She had already arranged to pick up her children from school early, so we had to collect them, but she took a lateral flow test before we left to do that. It showed negative. At her workplace they take lateral flow tests twice a week and she had been negative all the time. We picked up the children and sat in the car debating what to do, then rang our Cumbrian relatives and cancelled the trip. Early the following morning she took a PCR test which showed her to be positive. The lateral flow test was still showing negative and has continued to do so for several days now since the PCR test. I also took a PCR test since I had been in close contact with her for a couple of hours. Luckily it was negative, but I am now keeping out of everyone's way in Covid quarantine for 10 days.
She has now lost all faith in the lateral flow tests. We are now wondering whether these large gatherings (football matches, Wimbledon, concerts, etc.) which require a negative test result from attendees are actually demanding PCR tests or just lateral flow tests. If the latter, expect an increase in the number of infections recorded - oh, wait a minute, isn't that what is happening now.....?
