He said despite claims by Remainers, Ireland and EU negotiators, his past experience as an immigration minister showed there is no need for a “hard border” between Ireland and Northern Ireland.
His intervention comes after a leaked email revealed Democratic Unionist Party leader Arlene Foster is prepared for a Brexit “no deal”.
Mr Harper said Theresa May, heading to Brussels on Wednesday for crunch Brexit talks, needed to remind European leaders that they had already agreed there will be no border between Britain and Northern Ireland. The Prime Minister is under pressure to agree a backstop deal to keep the province under EU rule as part of its customs union, to deal with the Irish border.
But this would create a customs border with the rest of the UK and could also fuel claims for a separate deal for Scotland and Wales.
Mr Harper says the backstop text “explicitly says that there is a ‘commitment to preserving the integrity of’ the United Kingdom’s internal market and Northern Ireland’s place within it and also that ‘in all circumstances, the United Kingdom will continue to ensure the same unfettered access for Northern Ireland’s businesses to the whole of the United Kingdom internal market'”.
He added: This commitment is crucially important across Northern Ireland as more than 85 per cent of sales in goods and services is made up of business activity within the UK internal market – either internally within Northern Ireland or between Northern Ireland and Great Britain.”
Mr Harper said the EU had interpreted December’s backstop “to suit itself, effectively demanding a border in the Irish Sea in what amounts to a de facto annexation of Northern Ireland by the EU”.
He described it as “a flagrant breach of both the Belfast Agreement as well as the territorial and constitutional integrity of the United Kingdom” and argued that a computer-based solution proposed by the UK was the only way to deal with the issue.