The full comment/paper published in the Sept 29th 2020 Respiratory Medicine section of The Lancet is available here, though the most interesting sentences read:

The current rate of operational false-positive swab tests in the UK is unknown; preliminary estimates show it could be somewhere between 0·8% and 4·0%.2,6 This rate could translate into a significant proportion of false-positive results daily due to the current low prevalence of the virus in the UK population, adversely affecting the positive predictive value of the test.

A false positive PCR rate of between 0.8-4.0% potentially represents between 800 and 4000 false positives per 100,000 tests - presuming those 100,000 tested individuals are all free of CV19. Essentially, the lower the actual incidence of infection in a tested population is, the more significant the false positive rate becomes - and visa-verse. For example, if on the other hand 100,000 tests were carried out on a set of individuals more likely to be infected, the false positive rate becomes less significant.

Given as of today (week 46), the UK case rate (i.e. positive PCR tests) per 100,000 individuals is reported here as 471.3. Thus given that the hypothesized false positive rate is between 800 and 4000, we can presume it is likely very significant at the present time. The deaths per 100,000 individuals is listed as 9, for the same week 46.

It is also important to bear in mind that the PCR test has not been proven to test purely for what is being termed CV19, as opposed to just picking up general genetic material (including potentially, other corona viruses).