The DUP, which walked out of the power-sharing government in protest at the protocol, argues that it is driving a wedge between Northern Ireland and the rest of the UK. Britain and the EU are also in protocol negotiations over cutting the number of customs controls faced by British goods entering Northern Ireland.

There has been an uneasy truce since Liz Truss, the Foreign Secretary, dialled down British threats to suspend parts of the protocol by triggering Article 16, but the supplanting of British law in Northern Ireland is likely to reignite calls from Tory backbenchers for Article 16 to be invoked. 

Brussels has warned that such a move would risk the EU cancelling its trade deal with the UK.

Northern Ireland Executive officials have told London they resent being ripped out of the CTDA and warned there could be fewer or lower quality Covid tests in the province as a result. Most of Northern Ireland’s supplies of tests come from Britain, which increases the risk of shortages.

Ireland, which could supply EU-compliant tests, put limits on sales of tests during the most recent surge of the virus.

Using the national stockpile to make up a Northern Irish test shortage would risk crippling the UK’s emergency response to a new Covid variant, officials warned in documents obtained by The Telegraph.

“Using the stock in this scenario would significantly weaken the UK-wide contingency response if such a response were needed,” one said. The tests would still need to comply with the new EU standards, it added, before describing the risk of shortages as “small”.