Key issues at very heart of the crisis

WHY IS THE BORDER SO IMPORTANT TO TALKS?

After Brexit, it will become the UK’S only land border with the EU. How that frontier is managed is one of the three key issues the EU wants assurances on – along with citizens’ rights and the “divorce bill”.

It is proving the most difficult to resolve, with economic and social factors mixing with potent historical and political considerations.

WHY ARE THERE SUCH FEARS BREXIT WOULD CHANGE THE CURRENT BORDER?

If the UK left the EU but remained in the single market and customs union the border problem might not be so complex.

But the UK’S decision to leave Europe’s trading and free movement frameworks mean the border is set to become a crossing point between two different regulatory and economic zones.

This has prompted fears of a “hard border”, with a return to check points – albeit for very different reasons to those erected during the Troubles.

Some even fear a hardening of the border could reignite violence.

WHAT DOES THE EU WANT?

Brussels insists the retention of a “soft” border can only be achieved if either the whole of the UK, or just the North, remain within the single market and customs union, or a specially-tailored system that complies with EU regulations. This is the Government’s preferred option.

WHY IS THIS SUCH A PROBLEM FOR THE UK?

The UK government’s existence is dependent on its deal with the DUP. While 56% of the North voted Remain, the DUP campaigned for Brexit and is set against anything that would see the region treated differently to the rest of the UK.

To do otherwise, it claims, would draw a border up the Irish Sea. The DUP even accused Dublin of pushing for regulatory alignment as a backdoor bid to a united Ireland.

Reports that No 10 would agree the North would continue to adhere to EU regulations post-brexit were rejected by the DUP.

SO DOES THE DUP HOLD ALL THE CARDS?

Not quite. If its 10 MPS pulled put of their deal with the Tories, they would lose influence at Westminster – endangering a linked €1.1billion of Treasury funding – and face the prospect of “pro Irish republican” Jeremy Corbyn winning a snap general election.

ARE MRS MAY’S PROBLEMS CONFINED TO THE NORTH?

No. A different regulatory regime for the North prompted demands for the same from Scottish First Minister Nicola Sturgeon and London mayor Sadiq Khan.