Britain's Prime Minister Boris Johnson on Thursday said last-gasp talks for a Brexit trade deal with the European Union could fail, and urged the public to prepare for a "no deal".

"There's now a strong possibility... that we will have a solution that's much more like an Australian relationship with the EU than a Canadian," he said.

Britain left the European Union in January, ending nearly 50 years of integration with its closest neighbours and biggest overall trading partner.

UK and EU negotiators were on Wednesday given another 72 hours to come to an agreement on their future trading relationship before a decision on whether to continue on Sunday.

Whatever happens, Britain will leave the EU single market and customs area on January 1. With no deal - like Australia - it will trade on World Trade Organisation terms, with tariffs and quotas.

Johnson's remarks came after he updated his cabinet of ministers on his dinner talks with European Commission president Ursula von der Leyen in Brussels on Wednesday night.

"They agreed very strongly with me that the deal on the table is really not at the moment right for the UK," he said.

He blamed Brussels for seeking to "punish" Britain if it did not keep in lockstep with any new future EU legislation, despite having apparently taken that demand off the table previously.

Johnson said such "equivalence" rules to ensure fair competition were "not the sensible way to proceed" and had no counterpart in other trade deals.

"It's a way of keeping the UK kind of locked in the EU's... regulatory orbit," he said.

That, and proposals for continued EU access to UK fishing grounds, were not in keeping with Britain's status as a sovereign nation.

But Johnson said Britain was not on the point of abandoning talks altogether. "We'll go the extra mile.

"I will go to Brussels, I will go to Paris, I will go to Berlin, I will go to wherever to try to get this home and get a deal.

"We're not stopping talks, we'll continue to negotiate but looking at where we are, I do think it's vital that everyone now gets ready for that Australian option."

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