Foreign Secretary Dominic Raab has refused to close the door on the possibility of the trade talks with the European Union continuing past the Sunday deadline.
The Cabinet minister said “never say never” and highlighted that negotiations with Brussels have a tendency to “drag and drift”.
Prime Minister Boris Johnson was expected to have a telephone call with European Commission president Ursula von der Leyen at 11am after negotiations re-started in the Belgian capital at 8am UK time.
The two leaders had agreed during a dinner meeting last week that Sunday marked the deadline for a “firm decision” to be “taken about the future of the talks”, opening up the possibility that the negotiations could be collapsed without an agreement.
However Mr Raab, in comments made to broadcasters, suggested there could be room for manoeuvre on the end point of the negotiations over a free trade agreement.
He said there is “a long way to go” to find a resolution on the two outstanding issues of fisheries and so-called level playing field “ratchet” clause which would tie the UK to future EU standards.
But the former Brexit secretary added that discussions could continue past Sunday if Mr Johnson and Europe’s top official are able to break the deadlock during their conversation.
The Cabinet minister told BBC One’s Andrew Marr Show: “The bar is quite high for us to be able to keep talking.
“We would need at a political level a commitment to move on those two key issues.
“When you look at what I said at the start of the week, it is pretty similar to what I’m saying now, which is never say never because EU negotiations can often drag and drift.
“But actually we do need finality and therefore we need at the political level of Ursula von der Leyen, the president of the European Commission, that there is clarity the EU will move on those two key issues. If we get that then there are still talks to be processed.”
Sir Ivan Rogers, Britain’s former ambassador to the EU, said he suspected there would be movement on the deadline.
“I think it’s odds against today, but I’m not sure the talks will break down today either,” he told Sky News’ Sophy Ridge On Sunday programme.
“Most of these deadlines in Brexit over many years have carried on being broken and I suspect this might be the latest, but we will see.”
The possibility of a delay comes amid a row over fisheries after the UK and France clashed over what future arrangements should look like in terms of allowing European trawlers to access British territorial waters.
French President Emmanuel Macron is said to have threatened to veto a UK-EU trade deal after expressing dissatisfaction at the new quota terms being thrashed out for his fishermen.
Mr Raab told Marr it is “crazy” of the French to make “aggressive demands” when a no-deal scenario would leave their boats with “zero assured access” to UK fishing grounds.
The Government has also sparked anger after confirming that four Royal Navy gunboats have been placed on stand-by to guard British waters from EU trawlers if there is no agreement.
First Secretary of State Mr Raab said the UK is “going to exercise full control in the way I think people would expect over our fisheries” but said any enforcement would be “proportionate”.
But Spanish foreign minister Arancha Gonzalez said she does not believe the proposition of deploying gunboats is “serious”.
She told the Sophy Ridge programme: “I think this is all for the gallery, I don’t think this is serious – and, by the way, I don’t think this is needed.
“I think what would be more responsible is to sit down and agree what kind of relationship does the UK want with the European Union on fishing, again understanding that on this, like on the rest (of the issues), there are things for the UK to win, things for the EU to win – we just have to find this middle point.”
Former Labour leader Ed Miliband said a no-deal Brexit would be “a disastrous outcome for the country”.
The shadow business secretary told Marr it would mean “tariffs across the board”, while the British Chambers of Commerce president Baroness Ruby McGregor-Smith warned it was difficult for businesses to plan without knowing whether they faced extra charges or restrictions when trading.
But Scottish Office minister David Duguid played down the impact of tariffs, describing them as “not necessarily the end of the world”.
He told the BBC: “We export from countries we don’t have free trade agreements with, on Australia terms for example which is the expression often used. It doesn’t stop exports, it doesn’t stop trade.”