The UK’s competition watchdog has warned PCR test providers to “immediately review their practices” or face enforcement action if they treat customers unfairly.

In an open letter, the Competition and Markets Authority (CMA) warns companies within the sector that their actions could breach consumer protection law and suggests the Department of Health and Social Care (DHSC) “could consider to address concerns over the price and reliability of PCR test and the quality of service people receive”.

It follows a review into the PCR testing market by the regulator which found evidence of customers facing additional charges which were not advertised, not receiving their tests or results at all and failing to receive refunds when a quality service was not provided.

It comes as holidaymakers have expressed concerns about excessive costs for tests during the August high season.

The government announced earlier this week that it would be warning 82 companies that they could be removed from the Gov.uk list of authorised providers if they advertise misleading prices.

The letter, published on Wednesday, instructs PCR COVID test providers to review their policies to make sure they are in line with the requirements of consumer law and to make any changes where necessary.

The “practices of concern” to the CMA include:

• Advertising up-front prices for PCR tests which do not include additional charges that everyone must pay

• Advertising cheap PCR tests which are only actually available in very small quantities or are not available at all

• Failing to deliver PCR tests or provide results within stated timescales, or at all

• Refusing to provide consumers with refunds where tests are not provided within advertised and/or agreed timescales, or at all

The letter lists 11 steps providers should take to improve their practices, and includes not focusing their advertising on cheap tests which are only available in small numbers, showing the full cost of tests including all compulsory charges and providing “honest, accurate and clear” timescales on when tests will be received.

The CMA add that PCR test providers should also ensure that both tests and results are provided within the advertised timescales.

CMA general counsel Sarah Cardell said: “PCR test providers should be in no doubt that they need to get on the right side of the law. If they don’t, they risk enforcement action.

“Our advice today will also help people by setting out exactly what they should expect for their money.

“This warning goes hand-in-hand with action taken by government this week and is the latest step in our work to tackle rip-off prices and bad service.

“We continue to work closely with DHSC in reviewing this market and will be providing further advice to DHSC on action that can be taken.”

A separate investigation by consultancy Fideres found the cheapest travel test providers on the government’s official list have the biggest gap between advertised and actual prices.

It also discovered that many providers listed did not have tests to order.

Earlier this month, Health Secretary Sajid Javid announced that the price of PCR COVID tests provided for travel would fall by £20 for one test to £68.

The sum would decrease by £35 for two tests, making the total £138.

But Conservative MP Henry Smith, chairman of the all-party parliamentary group on aviation, said private PCR tests should be capped at £40.

The health secretary had asked the competition watchdog to investigate the market for PCR tests due to concerns about “exploitative practices” and inadequate service.

The government say the tests are needed for travellers to protect public health.