Two companies are being sued by the British government for over £145m after they allegedly supplied defective COVID-19 tests.

The government has told the High Court that the tests "failed at an unacceptable rate" but the companies deny the accusations and claim the tests were effective. The Department of Health and Social Care (DHSC) is reportedly seeking a refund for thousands of COVID tests that were produced by the companies Primer Design Ltd and Novacyt.

The two companies face accusations that they breached a contract signed in 2020 due to "unduly high" levels of test failures. The companies have launched a counter legal claim against the government to recover £70m they say is owed to them.

Adam Heppinstall KC, representing the DHSC, told the court that: "The failure rate is far in excess of anything that can be tolerated in a product." He continued: "Time is of the essence and the quality and robustness of the test is very important. A false negative is frankly very dangerous for public health.

"A test that does not work as often as this test did not work would slow down a laboratory to the point of uselessness, which in itself is a threat to public health." DHSC signed a contract with both companies in September 2020, before the second lockdown and the companies agreed to provide 6,300 'Exsig' COVID kits per week until January 2021, costing the government £145.9m before VAT. Before being distributed to the public, the COVID kits were tested by the Technologies Validation Group (TVG) which identified concerns.

Read more: Long COVID leaves distinctive signs in blood 'Next pandemic is around the corner' experts warn In November 2020, TVG deemed the tests should not be used and the kits were never rolled out across the NHS. "Exsig failed at an unacceptable rate due to design and/or manufacturing defects and therefore lacked robustness.