Mr Johnson has stated his desire to eliminate EU-imposed obstacles to the free movement of goods and agriproducts between Britain and Northern Ireland.

       In his letter, the former leader of the Ulster Unionists wrote: “The Northern Ireland Protocol has not only subverted the main safeguards within the Belfast Agreement causing civil unrest and political uncertainty, but it is also damaging the Northern Ireland economy disrupting supply chains, inflating prices and diverting trade from our main market in Great Britain.

       “At the heart of the Belfast Agreement is consent.

       "This means there can be no change to the constitutional position of NI as part of the UK without the agreement of a majority of the people of the country.

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       "But the Northern Ireland Protocol, by giving the EU powers over the movement of goods into and out of the Province, has torpedoed the ‘consent’ principle.

       "It also risks a return to sectarian strife.

       “The NIP totally destroyed this consent principle to the detriment of the unionist community.”

       Lord Trimble added that this “monumental constitutional change has been imposed on the people of NI without seeking their consent".

       He said it was "against the manifest opposition of every unionist party and politician in NI”.

       He added: “The result has been political unrest and violence and threats of further violence on our streets because the political promises of the Belfast Agreement have been flippantly dismissed through the NIP."

       Northern Ireland is currently in an extended grace period where the strictest customs conditions do not need to be enforced.

       This extension is due to run out at the end of September.