In a statement, the Scottish Conservative leader said: “If regulatory alignment in a number of specific areas is the requirement for a frictionless border, then the Prime Minister should conclude this on a UK-wide basis”.
She suggested that providing one part of the UK with a special deal in the Brexit negotiations would compromise the political, economic and constitutional integrity of the union.
Ms Davidson’s comments came after Theresa May was forced to leave Brussels on Monday with no agreement. Her hopes to move the negotiations onto phase two – discussing a future relationship and trade – were derailed after the Democratic Unionist Party (DUP) rejected the deal on the cards at the eleventh hour.
The party – responsible for propping up Ms May’s fragile Government – appeared to be blindsided by the UK’s apparent concession of “regulatory alignment” on both sides of the border, to avoid checks in Ireland.
She added: “The question on the Brexit ballot paper asked voters whether the UK should stay or leave the European Union – it did not ask if the country should be divided by different deals for the different home nations.
“While I recognise the complexity of the current negotiations, no government of the Conservative and Unionist Party should countenance any deal that compromises the political, economic or social integrity of the Untied Kingdom.
She added that all sides in the negotiations recognise the paramount importance of the Good Friday agreement and that there should not be a return of hard border in Ireland. “Similarly, jeopardising the UK’s own internal market is in no-one’s interest,” she added.
The comments from Ms Davidson, a vocal supporter of the campaign to remain inside the European Union in last year’s referendum, also came after the Tory MP Anna Soubry said that no Conservatives wanted Northern Ireland treated different from the rest of the UK, which she said would be “gift” to the Scottish National Party.
“Nobody could want one part of our country to have a different set of rules to another part of our country,” said Ms Soubry. “On that, everybody is agreed.”
Tory former attorney general Dominic Grieve added he would “never support” internal tariff customs borders within the UK, meaning it would be necessary for the whole country to remain in the customs union in order to maintain an open border in Ireland.
“The reality is that if we wish to maintain a non-border, then the regulatory alignment must apply to the whole country, the whole of us here,” he told BBC Radio 4's PM.
“I think it highlights the fact Brexit is proving to be immensely complex and difficult, and forgive my saying it, exactly as was predicted a year ago and ruthlessly disregarded by those who advocated leaving the EU, and we're going to have to do a reality check on what is in our national interest.
“That may require some of the idols that have been put up, such as our leaving the customs union, to be reconsidered."
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies