The UK operational false positive rate is unknown. There are no published studies on the operational false positive rate of any national COVID-19 testing programme.
An attempt has been made to estimate the likely false-positive rate of national COVID-19 testing programmes by examining data from published external quality assessments (EQAs) for RT-PCR assays for other RNA viruses carried out between 2004-2019 [7]. Results of 43 EQAs were examined, giving a median false positive rate of 2.3% (interquartile range 0.8-4.0%).
Alistair Haimes interpreted these results in this way:
2.3% false positive rate with 0.04% virus prevalence rate (ONS) means that if you test positive you have only a 4/234= 1.7% chance of being infected. We’re flying blind.
@AlistairHaimes. 3 July 2020
if the false positive rate is that high, surely they just know that it is ‘about nothing’; 0.04% must be false precision?
https://www.gov.uk/government/publications/gos-impact-of-false-positives-and-negatives-3-june-2020