The UK government said it was taking action against 82 PCR Covid test providers as part of a clampdown on “cowboy” pricing practices.
An initial investigation discovered that the companies were listing “misleading” lower prices on government websites than on their own.
Firms facing censure represent 18% of all the companies listed on the government’s PCR travel advisory website.
“It is absolutely unacceptable for any private testing company to be taking advantage of holidaymakers and today’s action clamps down on this cowboy behaviour,” said Health Secretary Sajid Javid.
He added that 57 firms would be removed from the government’s list and a further 82 given a two-strike warning, meaning they would be struck off they advertised misleading prices again.
Javid ordered a review by regulators after public outrage over the cost of PCR tests, which are required for international travel. The government has been criticised for allocating most of the contracts to the private sector.
He later reduced the cost of an official National Health Service (NHS) PCR test by more than a fifth in an attempt to drive down the market price.
The official test and trace package for international arrivals has been cut to £68 from £88 for green or fully vaccinated amber arrivals, and to £136 from £170 for two tests for amber arrivals who are not fully vaccinated.
Analysis by the Guardian newspaper indicated passengers to the UK have spent at least £500m on PCR Covid-19 tests from private companies since mid-May, but in some cases the NHS had been lumbered with extra costs when firms fail to deliver them.
All travellers returning from green- and amber-list countries must take a test before they depart for the UK, and a further PCR test on their second day after arriving home. With PCR tests costing upwards of £50 each, households are paying as much as £200 for day-two kits.
Research by car insurer Admiral found the UK was among the most expensive places in the world for PCR testing, with Britons spending an average of £92 on testing to go abroad.