The story about LFTs being unable or less able to detect the whatever the variant du jour is have been around since the beginning (remember that the initial story from some – fed by the usual suspects – was that LFTs were ineffective).They have proven to be consistently effective within the expected bounds of performance. All the ones I know about use polyclonal IgG antibodies that recognise a range of epitopes on the spike protein. As such it's far less sensitive to mutational changes than PCR (which relies on small regions of nucleic acid in which changes can have significant effects – this is why the standard PCR assay looks at three regions, and indeed, drops in binding efficiency have help track variants – there are QC processes and internal controls to monitor this).
LFTs are, of course, less sensitive; but counter to that PCR is in some circumstances oversensitive, detecting viral RNA long after infection (leading to those frothy 'omg, covid found in brain' stories, because yes, that's what happens post-viral infection, all that degraded viral nucleic acid from lysed and dying cells floats around in your blood and lymph, larger pieces removed through antibody binding and phagocytosis, the rest slowly degrading – there's no specific extracellular pathway to remove nucleic acid – till you piss it out, which may take days to weeks depending on initial viral load.
As Chris says, disputing known things isn't helpful, this is why I rag on Independent Sage who have driven a good degree of this misinformation (not to helped to politicised this amongst their many social media followers), and indeed, this approach drives counter misinformation all the way through to anti-vax propaganda. They should – but won't – take some responsibility for this.
The test works, and the sensible assumption, which is also known is that there isn't a lot of covid circulating so a negative test probably means you don't have covid. Everyone in the UK has significant and broad immunity through vaccine and exposure and it seems the virus has already exploited much of its ability to evade that immunity. There are, as there has always been, many other viruses which have, of course, taken the opportunity to spread again.
As ever sensible advice to avoid people and take time off work if ill, but we really ought to bear in mind (another unlearned lesson from the lockdown era where modestly affluent middle-class people made a virtue of outsourcing their risk to delivery drivers and the like), that the luxury of taking a week or two off work is just that for many people.
