Boris Johnson's Brexit deal will cause higher prices and less choice for customers in Northern Ireland if it is fully implemented, businesses have warned.
The latest warning, echoed by Marks and Spencer, chair Archie Norman comes ahead of government ministers unveiling their plans for the future of the agreement – which Britain is no longer happy with.
Ahead of the 2019 election Boris Johnson hailed the deal as an "oven-ready" success but the government now says it is causing major problems and needs to be changed.
Northern Ireland secretary Brandon Lewis will make a statement to the House of Commons at lunchtime spelling out the government's proposals for the protocol, which was designed to avoid a hard border with the Republic of Ireland.
The government is expected to warn that it could tear up the arrangements its agreed in 2019 and unilaterally override the deal if the EU does not comply with its demands.
Meanwhile Brexit minister Lord Frost, who personally negotiated the protocol but now says it is inconsistent and vague, will unveil a UK command paper explaining in more detail the UK's plans.
Brussels wants the UK to implement what it agreed to and – having already granted extra grace periods and extension to keep London happy – is likely to react angrily to the proposals. EU officials say there is no ambiguity in the text and that the UK is acting like an unreliable partner.
The arrangement cooked up by the UK and EU in 2019 puts checks down the Irish Sea between Great Britain and Northern Ireland, which are adding significant frictions to trade between different parts of the UK. There have been supply shortages of some goods in the province, with some businesses pulling out entirely due to the new Brexit bureaucracy.
In a letter to Lord Frost, M&S chair Mr Norman said "pointless" checks with the Republic of Ireland were "threatening" to its business there.
And he warned that when grace periods on applying more checks to Northern Ireland end in September, the chaos extending to that part of the UK could deepen.
He said new less flexible current customs and regulatory arrangements between the UK and EU, which were favoured by Boris Johnson's government during talks, are "totally unsuited and were never designed for a modern fresh food supply chain between closely intertwined trading partners".
Unlike most major countries that sit outside the EU, the UK has refused to sign up to single market or customs union rules – a decision which has made trade with the bloc much more difficult.
"There is no other outcome for consumers in Northern Ireland in the end other than higher prices, given the inflationary pressures being put on to retailers by the regulatory regime," Mr Norman wrote.
"Being able to keep the show on the road, let alone growing, is going to be very challenging."
The EU has proposed a temporary Swiss-style veterinary agreement to remove the vast majority of the checks, but the UK has rejected the idea.
The British government says aligning with EU rules in this area would be a breach of sovereignty, and ministers – who are fixated on doing trade deals with other countries – worry that aligning to this part of EU law would make it harder to sign agreements with countries like the US and Australia.
The UK is yet to explain how it will solve the problems while meeting the objectives of protocol.
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