Merriman put four questions to the health secretary in the letter sent on Wednesday (11 August) addressing PCR testing and genome sequencing.

He asked why only "25% or (6%) of the 415 PCR test providers in the UK have been accredited by the UK Accreditation Service (UKAS)". 

UKAS assesses the scientific and medical competence of organisations that provide certification, testing, inspection and calibration services.

Merriman also asked why the government website "does not direct consumers to accredited status [providers] and whether this will be amended".

On Tuesday (10 August), pictures of "overflowing and unsafe" PCR test drop boxes operated by private firm Randox were shared via Twitter.

Merriman queried whether the "effectiveness and security of personal data and testing and sequencing has been compromised for members of the public" whose tests were left outside the drop-off points.

While welcoming Javid’s request for the Competition and Markets Authority to carry out a review of the private testing market, Merriman urged the government to give "serious consideration to more affordable options".

"There needs to be a clear and compelling justification for continuing to mandate the use of PCR tests," he wrote. "They are an unnecessary barrier to affordable international travel."

Ben Bradshaw MP, who also sits on the Transport Select Committee, backed Merriman’s calls, saying "Johnson’s rip-off testing regime is unique in Europe", after claiming his family had recently paid 15 euros for tests required to return to Britain.

Merriman urged Javid to reply to the letter by 24 August.