British hopes of opening Brexit trade and transition talks this December were thrown into renewed doubt as it emerged that Ireland is making fresh demands over the Northern Ireland border question, the Telegraph can reveal.

The toughened Irish stance, reflected in a leaked European Commission document obtained by The Telegraph, blindsided British officials at Brexit negotiations in Brussels on Thursday as Ireland piled on pressure in the talks.

British officials had believed that question of how to avoid creating a hard Irish border when the UK quits the EU single market and customs union had been ‘parked’ until the EU opened talks over trade and the future relationship.

However the leaked talking points paper entitled ‘Dialogue on Ireland/Northern Ireland’ shows Ireland is now pushing hard for concrete reassurance on the Irish border question ahead of the crucial EU leaders’ summit in December.

The one-page paper states that in order to preserve the Good Friday Agreement peace deal, the Brexit divorce deal must respect “the integrity of the internal market and the customs union”, of which Ireland will remain a member.

It adds that it is “essential” that the UK commits to avoiding a hard border by remaining part of the EU Customs Union and continues to abide by the “rules of the internal market and customs union”.