The chief negotiators from the European Union and United Kingdom on Sunday continued efforts to reach a deal on the UK's future trading relationship with the bloc as a self-imposed deadline loomed at the end of the day.

The EU's Michel Barnier and the UK's David Frost started talks just after dawn in a final bid to reach agreement. Talks have already been running for almost a year.

Frost reportedly left the talks after 1 1/2 hours to return to the UK diplomatic mission in Brussels.

UK Prime Minister Boris Johnson and European Commission President Ursula von der Leyen are expected to talk around midday on Sunday to discuss the progess of the talks. They are then to issue a statement on whether to abandon the talks.

A news agency quoted sources within the bloc are saying that the two leaders were expected to call for trade talks to continue.

German Chancellor Angela Merkel has said everthing that is possible should be done to reach a deal.

Sunday's deadline is just the last in a series of such cutoff dates, but time is running short, with a transition period due to end on December 31.

Hardened stances

The UK officially left the EU on January 31 but trade and other sectors remain within the bloc's structures until the end of the year.

Talks on a deal have so far failed largely because of the UK's insistence that it should trade with the bloc with as few restraints as possible and the EU's equally obstinate stance that Britain must stick to EU rules to ensure fair competition.

The UK claims the EU is wanting to thwart Britain's status as an independent and sovereign nation by forcing it to obey the bloc's rules. The EU, in turn, fears that Britain could drastically lower its social and environmental standards while subsidizing UK industry with state money, thus creating a low-regulation economic rival hovering at its margins.

British Foreign Secretary Dominic Raab said on Sunday that there was probably "a long way to go."

Likely chaos

If the negotiations on Sunday prove fruitless once more, time will be short to prepare for likely chaos on January 1, with imports into and exports out of the UK negatively affected.

Without a deal, the UK will have to trade with the EU under World Trade Organization rules — a system British Prime Minister Boris Johnson has been euphemistically calling the "Australian" model. That would entail numerous tariffs and barriers.

Other issues hampering the talks have been differences over the legal oversight of any deal and fishing rights in UK waters.

Johnson, who says it is "very, very likely" that negotiations will fail, insists the UK will thrive whether or not a deal is reached.