Boris Johnson: Only over my dead body will there be a border in the Irish Sea

He said it was important to have the Northern Ireland protocol, which ensures the Province follows some of the EU’s rules to allow freedom of movement of goods and services across the Irish border.

Business leaders in Northern Ireland have voiced fears red tape on goods crossing from Great Britain may make some trade unviable.

The next round of Brexit talks will begin on August 18 between the prime minister’s adviser David Frost and the EU.

In a tweet, Mr Frost said: “Our assessment is that agreement can be reached in September and we will work to achieve this if we can.”

Under the protocol, if no wider trade deal is secured with the EU, tariffs would be paid on goods travelling from GB into the Republic of Ireland and the rest of the EU via Northern Ireland.

Which goods are at risk of doing so has still to be decided in negotiations, with the EU keen to ensure Northern Ireland does not become a backdoor into its single market.

The government has insisted a £355m package to help Northern Ireland’s businesses navigate Brexit red tape is not an admission of an Irish Sea border.

Meanwhile, Larne port is preparing to install a border control post (border posts are facilities used to check animals and food arriving in the EU single market).