The EU will threaten Theresa May’s Brexit plan on Wednesday by warning that Northern Ireland must sign up to Brussels rules and regulations if Britain wishes to leave the customs union and single market.

France and Germany are understood to have blocked British plans to continue “fudging” the issue and are now insisting on a legal agreement, which is likely to spark an “explosive row” in the coming days.

The DUP, which props up the Conservative minority government in Westminster, will strongly oppose the EU’s proposal, as will Conservative Brexiteers.

British Brexit negotiators privately warn that the hardline stance from Brussels has left them unable to negotiate.

The Telegraph understands that the approach will be set out in the European Commission’s draft withdrawal agreement, which is due to be published Wednesday.