Positive results from UK single gene PCR testing for SARS-COV-2 may be inconclusive, negative or detecting past infections.

“Without diagnostic validation it is not clear what can be concluded from a positive PCR test resulting from a single target gene call, especially if there was no confirmatory testing. Many of the reported positive results may be inconclusive, negative or from people who suffered past infection for SARS-COV-2. Even with diagnostic validation of the single target gene call, the UK lighthouse laboratories appear not to be in strict conformance with the WHO emergency use assessment and the manufacturer instructions for use. Given this it is clear the ONS and the UK lighthouse laboratories needs to publicly clarify their use of, and justify the reasons for, deviating from these standards.”

https://www.bmj.com/content/372/bmj.n208/rr-3