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.