The Democratic Unionist Party has warned UK Prime Minister Theresa May it will bring down her government if Northern Ireland is forced to stay inside the EU customs union and single market after Brexit. The renewed threat comes ahead of a vote by British MPs, pushed for by pro-EU parliamentarians, seeking to keep UK customs union membership.
It also follows increasing signals from the Brexit talks in Brussels about a formula of language for a face-saving deal aimed at Brexiteers, keeping closest EU-UK trading links after Brexit happens and effectively mimicking British customs union membership.
Brussels diplomats say that, as things stand, the UK would only get a Canada-style deal with the EU after Brexit, which would not avoid a return of the Border in Ireland.
Nigel Dodds, who heads the DUP in the London parliament, said his party will vote against Mrs May's minority Conservative government if any of these so-called red lines on Brexit are crossed.
Mrs May has pledged that Brexit means leaving both the single market and the customs union, and these are deemed among the red lines.
As time continues to run short, the EU and the UK appear deadlocked on how to avoid a so-called 'hard Border' in Ireland, if Brexit really means Britain leaving the customs union and single market.
The UK is set to leave the EU in March 2019, but a transition period will delay this until December 2021. The so-called 'Withdrawal Agreement' mapping most of this out is set to be cleared at an EU leaders' summit next October.
The DUP's belligerence on the issue was outlined by Mr Dodds in comments to the British Conservative Party website.
Mr Dodds said if the North was treated any differently from any other part of the UK under Brexit, his party would vote against Mrs May's minority government which they have been propping up in office.
UK Brexit Minister David Davis told a parliament committee that he would deem himself to have failed if the Brexit outcome left the UK within the EU customs union.
Membership of the customs union would mean London still collecting import tariffs from non-EU states' exports to Britain on behalf of Brussels and would also limit Britain making trade deals beyond the EU.
Both of these were major themes in the 2016 referendum campaign that culminated in the UK voters' decision to quit the EU after 40-plus years of membership.