Northern Irish sausage makers can supply both the UK and EU markets thanks to the protocol, and many major supermarkets use domestic suppliers.

But the prospect of British sausages being banned in Northern Ireland brought both sides to the brink of a trade war in the summer.

Brussels warned it would hit back with tariffs if the UK carried out its threat to suspend parts of the protocol to secure British sausage supplies by triggering Article 16 of the treaty.

The battle became symbolic of wider issues with the protocol. Lord Frost accused it of having a chilling effect on British trade to Northern Ireland and Unionists fear it drives a wedge between them and the rest of the UK.

The European Commission’s October offer on sausages and to slash customs checks on British goods kickstarted intense talks over the protocol.

A fourth round of negotiations continues this week but there is growing pessimism in Brussels after previous rounds failed to bring an expected breakthrough on medicines supplies.

‘It does seem like Lord Frost is out to steal our Christmas’

EU officials fear that Lord Frost will let negotiations drag through Christmas for a second year running.  

“As a diplomat I couldn’t call the British negotiator a grinch. But it does seem like he’s out to steal our Christmas once again,” said one envoy, who added many EU capitals thought the UK still planned to trigger Article 16.

The Royal Navy and Royal Marines last week carried out training exercises to simulate breaking up French port blockades by fishermen furious over post Brexit fishing licences.

The exercise, held to the backdrop of escalating tensions between the UK and France, follows the blockade of St Helier on Jersey by a flotilla of French fishermen in May.

A government spokesperson said: “This was a routine and long-planned exercise designed to improve our maritime security and resilience.”