The Competition Watchdog is set to probe eye-watering fees for PCR tests as holiday-makers are hit with huge bills.
The Competition and Markets Authority has pledged to investigate after a letter from Health Secretary Sajid Javid complained of varying prices for tests and “exploitative behaviour” and “unfair practices” by some 420 firms.
The tests are required for all travellers returning from amber and green countries, regardless of whether they are double jabbed.
France, Austria, Germany, Latvia, Norway, Romania, Slovenia and Slovakia were added to the green list at 4am on Sunday.
Spain, India, Bahrain, Qatar and the United Arab Emirates are now among the long list of on amber countries.

The tests are costing sun-seekers an average of £75 per person but similar tests are selling online for as little as £30 or as much as £270.
In France the average cost is £42 while in Greece it is less than £40.
“The cost of PCR testing can act as a barrier, especially for families who want to travel together,” Mr Javid wrote in a letter to CMA chief executive Andrea Coscelli, calling for a “a rapid high-level review”.
He added: “It is not right if some families experience yet further disruption unnecessarily because of practices in the market for private travel tests.”
Mr Javid has suggested the Government would be prepared to act against firms slapping “unnecessary costs” on consumers or those pushing “low quality” tests.

Figures released last week showed that a staggering £35 million had been paid for 500,000 tests, of which just 6,977 were positive.
Huw Merriman, Tory chairman of the transport committee, said on Friday he suspected that “expensive PCR tests for travel are an unnecessary rip-off”.
Transport Secretary Grant Shapps has said PCR tests are “helpful” in tracking new, and potentially more infectious, variants.
“We look forward to providing the secretary of state with advice on how best to ensure that travellers have access to tests that are affordable and reliable,” the CMA said.