Deputy leader Simon Coveney says power cannot be given to one party in Northern Ireland

The Democratic Unionist party cannot be allowed to veto any Brexit deal on the Irish border, Ireland’s deputy prime minister has said.

Simon Coveney spoke out after Theresa May disclosed that she was considering the option of giving the Northern Ireland devolved government a veto on any proposed regulatory barrier between itself and the rest of the UK.

The Sun reported on Saturday that the prime minister was pushing for an alternative set of regulatory arrangements for Northern Ireland, but that this was being blocked by the DUP, which is propping up her government. Coveney said: “We cannot allow one party in Northern Ireland to veto any proposals.”

He told RTÉ’s Marian Finucane radio show: “The British government has a confidence and supply arrangement with the DUP, but we don’t have a confidence and supply agreement with any one party in Northern Ireland.”

Speculation is growing that the EU and the British government are working on a “backstop to a backstop” to resolve the impasse in Brexit negotiations over the Irish border.

On Friday, May revealed she would be setting out the UK’s alternative, which would involve an element of decision-making power being wielded by Belfast.

“It will be in line with the commitments we made back in December – including the commitment that no new regulatory barriers should be created between Northern Ireland and the rest of the UK unless the Northern Ireland executive and assembly agree,” she said in her statement.

The assembly has not been functioning since power-sharing collapsed in Northern Ireland almost two years ago because of a dispute between the DUP and Sinn Féin. It is highly unlikely that Stormont will be restored to full operation before a Brexit deal is sealed.

May rejected the EU’s proposed wording for the backstop proposal in February because it would require the region to stay in the EU system even if the UK crashed out with no deal.

Coveney told RTÉ there was “no question of a border down the Irish Sea”, but he was keen to ensure that minimal checks were required on goods. “There are practical realities of trade, and we are trying to do that in a way that doesn’t undermine the constitutional integrity of the United Kingdom in a way that is threatening to unionism, but that can protect the concerns of both unionists and nationalists, neither of whom want a border re-emerging on the island of Ireland.”

He said he believed the DUP recognised that Northern Ireland was not the same “as Kent or a borough in London” and it had many differences from other parts of the UK.

The Daily Telegraph reported on Saturday that the “third option” for Northern Ireland would focus on extending the current regulatory checks on animals to other sectors. To protect the island of Ireland from outbreaks of disease, such as TB or mad cow disease, routine checks are done on livestock being imported from Britain, north and south of the border.

The DUP has accepted that these “sanitary checks” are in place but are opposed to extending this to non-agricultural goods.

Ireland’s taoiseach, Leo Varadkar, confirmed in Salzburg that the EU was reworking the backstop proposal to say that agriculture and phyto-sanitary checks would be the only physical controls that needed to take place between Northern Ireland and the rest of the UK.

In this scenario, customs declaration forms would be filed to tax authorities electronically, and the separate customs checks needed to prevent tax evasion and smuggling would continue.

It is argued that these checks are usually intelligence-led, based on tips-offs to the Police Service of Northern Ireland or Garda Síochána, and are part of the existing cooperation arrangements.