The EU has focused attention on Britain’s dysfunctional political system as a roadblock to progress in Brexit talks – warning that the UK needs to work out its internal differences to reach a deal.

Speaking the day after the shock failure of Theresa May to make progress after face-to-face meetings in Brussels, a spokesperson for the European Commission warned that “the show is now in London” as far as Brexit was concerned.

It comes after the DUP torpedoed a deal previously agreed by the Prime Minister with the EU on the Irish border – with DUP leader Arlene Foster apparently telephoning the PM while she was meeting with EU president Jean-Claude Juncker.

The DUP, which only has 10 MPs and won less than 1 per cent of the national vote, holds an effective veto on many government policies because Ms May is relying on them for a majority in the House of Commons.

The European Commission spokesperson told reporters in Brussels: “We have a common understanding with the United Kingdom on most of the relevant issues but there are some topics still open which will need further consultation and negotiation, notably in London. The show is now in London.”

The spokesperson would not confirm when Ms May would return to Brussels for more talks. Negotiations to convince the DUP to back the Government are already underway.

Theresa May's EU deal under threat from DUP over Northern Ireland border dispute

Ms May’s insistence on taking the UK out of the customs union and single market as part of Brexit has caused a major difficulty at the Irish border, because the Good Friday agreement – supported by all sides – stipulates that it must not be a hard border.

Theresa May with DUP leader Arlene Foster (PA Wire/PA Images) (PA)

Leaving the EU customs union however means customs checks must be implemented between the EU customs union – which the Republic of Ireland is a part of – and the UK.

A draft text jointly agreed by both sides, drawn up to solve this problem, and obtained by the Irish public broadcaster RTE on Monday read: “In the absence of agreed solutions the UK will ensure that there continues to be no divergence from those rules of the internal market and the customs union which, now or in the future, support North South cooperation and the protection of the Good Friday Agreement.”

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

But after the draft leaked Arlene Foster, the DUP leader, ruled out any move “which separates Northern Ireland economically or politically from the rest of the United Kingdom”.