EU negotiators believe that the Brexit process could be delayed by one year if the British government continues to demand trade discussions before its exit terms have been agreed to.

This is part of a long-running disagreement between the UK and the EU. Ms May and the Conservative Party want trade talks to happen in tandem with the drafting of the UK's complex exit deal.

"If they don’t accept the phased negotiations then we will take a year to draw up a new set of negotiating guidelines for Barnier," one senior EU diplomat told The Guardian.

"We don’t know when Brexit talks start. We know when they must end. Do your best to avoid a ‘no deal’ as result of ‘no negotiations," European Council President Donald Tusk tweeted following last week's General Election in the UK.

The future rights of UK citizens in the EU and EU citizens in the UK - and provisions for the Irish border after Brexit - are among the issues which the EU wants to resolve before beginning trade talks.

A source from the EU also told the news outlet that British officials have been briefed on the EU's negotiating stances for months, adding, "May has known about the sequencing of talks since last September. None of this has been a surprise to her."

The Conservative Party is now under pressure to form a new government ahead of the scheduled start of Brexit negotiations on June 19th.