Which GP was that, and what surgery? It's probably worth reporting that to the NHS/ PHE and maybe thinking about getting a new GP, as they've seemingly gone rogue against the NHS or PHE advice. Either that, or you're maybe misunderstanding, and incorrectly amplifying what they've said.
The LFT has a shorter working range than a PCR, but to say they're a waste of time is completely ludicrous. There's only about half a day where a PCR would pick up the virus before the LFT, but seeing as you have to wait 24 hours to get it, then it kind of nullifies that. The LFT covers the entitre infectious period also, and even shows varying degrees of infection, as the line gets fainter and fainter.
Advice now is to take an LFT right before meeting someone at higher risk, ie don't do it the night before or on the morning, literally do it half an hour before.
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