The government has privately conceded there will be post-Brexit checks on goods crossing the Irish Sea, months after Boris Johnson insisted there would be no such trade barriers. In a letter to the executive office in Stormont the government confirmed there would be border control posts in three ports, Belfast, Warrenpoint and Larne. Declan Kearney, one of the two junior ministers in the executive office, the regional equivalent of the Cabinet Office in London, confirmed the details at a select committee session in Belfast on Wednesday. He told members of the local assembly that officials had briefed the executive on Monday. “The sum total of that, and without breaching executive confidentiality … [is that the] British government has confirmed it will urgently put in place detailed plans with the executive, which does include the physical posts at ports of entry,” said Kearney. The prime minister agreed checks on goods entering Northern Ireland from Great Britain in a breakthrough meeting in Wirral with his Irish counterpart, Leo Varadkar, last October. However he was then accused of misleading the public after he was recorded on video telling local businesses weeks later that there would be no checks. If any business was asked to fill in extra paperwork, they should telephone the prime minister “and I will direct them to throw that form in the bin”, he told them. The Northern Irish protocol is part of the withdrawal agreement signed in January after Johnson led the Conservative party to an 80-seat majority in December. It will kick in next year whether there is a deal on trade or not. The EU had become increasingly exasperated with Johnson’s claims that there would be no checks. Fears that the UK would backslide on the deal were fuelled by the refusal of Johnson’s government to allow the EU to open an office in Belfast to help implement and enforce the protocol. The paymaster general, Penny Mordaunt, told the EU such a presence would be “divisive in political and community terms”. The Brexit deal is unpopular across the political spectrum in Northern Ireland because of the extra costs and bureaucracy it will entail for businesses. But it also means checks on the border with the Republic of Ireland will be avoided, something that has the support of Sinn Féin, and that exporters will have access to both the domestic and EU single market. The South Down Sinn Féin MP, Chris Hazzard, has said the British government must live up to the commitments made on Brexit, particularly in relation to the Irish protocol. “The British government cannot be allowed to renege on their legal obligations and must now work with the EU and the executive to ensure those commitments are fulfilled as a matter of urgency,” he said. Business have called for some of the paperwork including the entry and exit declaration forms for imports and exports to be waived, along with health certificates for each product coming to a local supermarket. Analysis by the Northern Ireland Retail Consortium of deliveries from Britain to high-street supermarket chains in Northern Ireland found that firms could incur costs of more than £100,000 per lorry unless special Brexit derogations were agreed. A Cabinet Office spokesman said: “We have always been clear that there will be requirements for live animals and agri-food, building on what already happens at ports like Larne and Belfast. “We want to work with NI businesses and the executive to ensure new admin procedures are streamlined and efficient. The protocol puts legal obligations on both sides. We are committed to complying with ours, just as we expect the EU to comply with theirs.”