Guidance from HMRC states Covid tests are exempt from VAT, which amounts to 20% on the sale price, if administered by a registered health professional or if the test provider has sales of less than £85,000 a year.

An invoice for a £44.90 self-testing kit from Eurofins seen by The Guardian stated that zero VAT had been charged.

Another invoice for a home testing kit from Expert Medicals provided to a UK resident allegedly stated that £0 taxes had been charged while Nationwide Pathology reportedly charged £40 for a day two PCR test with an invoice making clear no "sales tax" had been added.

A testing company executive, who asked not to be named, reportedly told The Guardian he "feared the decision by some providers not to add VAT might be distorting competition" by allowing cheaper prices.

"The legal and tax advice we were given was that we should be charging VAT, which we do and always have," he added. "When we see competitors potentially not charging VAT and undercutting us by so much it is very frustrating."

TTG has approached Eurofins, Nationwide Pathology and Expert Medicals for comment.