Covid test companies face tougher fines from next week if they advertise misleading prices.
Health secretary Sajid Javid said he had acted after an investigation by the Competition and Markets Authority had found inflated prices among PCR test companies.
From 21 September, fixed fines of up to £10,000 will be issued to firms that breach rules.
Javid said he would "shortly" outline further changes “to ensure consumers are given the best tests at the very best prices”.
He added: “It is completely unacceptable for any private testing company to take advantage of holidaymakers and we are taking action to clamp down on cowboy behaviour.”
He said more culprits had been found since the CMA review.
“Through our regular reviews and spot-checks, we have identified even more providers that were messing around with costs and have now removed 91 providers from gov.uk and corrected inaccurate prices of 135 private providers who will be removed from the list if they advertise misleading prices again.”