Brussels has warned a Brexit delay is far from certain as it called for people to "finalise all preparations" for a no-deal divorce.

The EU's chief negotiator Michel Barnier turned up the heat with just ten days to go until the UK is due to leave the bloc and no agreement ratified yet by parliament.

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Prime Minister Theresa May is on the brink of writing a letter formally requesting a Brexit delay after MPs voted by a large majority to back the move.

But Sky News understands she refused to tell senior cabinet ministers this morning how long she will request for the extension of Article 50 - the EU's legal exit mechanism.


It will be made public in a letter to EU leaders expected to be published on Tuesday or Wednesday, ahead of a summit on Thursday.

Mr Barnier cautioned that delaying Brexit would mean more uncertainty and costs, and added it would not be approved "without a good reason".

He added that "everyone should now finalise all preparations for a no-deal scenario".

Addressing reports that Mrs May could ask for a short and long extension, to pull the UK out of the EU whenever she gets a deal ratified, Mr Barnier remarked: "It's either one or the other."

Irish foreign minister Simon Coveney also said: "I think people would be very foolish to assume that this is just some kind of political game and that an extension will automatically be facilitated."

Earlier, German Chancellor Angela Merkel German claimed the EU would "watch very attentively" to how the UK government reacts to what it has branded a "major constitutional crisis".

She refused to predict how the bloc would react, saying: "I cannot evaluate what it will be on Thursday - much too much is in flux."

Image: Angela Merkel claimed 'much too much is in flux'

A new obstacle to Mrs May getting approval from MPs for her withdrawal agreement was erected by House of Commons Speaker John Bercow.

He cited a centuries-old convention as he warned the government against bringing back the twice-defeated Brexit deal for another vote if it remains unchanged.

John Bercow blocks new vote on 'same' Brexit deal

Ms Merkel added: "I'll concede that I wasn't actively aware of the British parliament's rules of procedure from the 17th century, so I took note of this with interest yesterday."

Her European affairs minister Michael Roth, who met with his EU counterparts in Brussels ahead of Thursday's gathering of the bloc's heads of government, sent a sterner warning to UK MPs.

"Dear friends in London, please deliver. The clock is ticking," he said.

Mr Roth called for "clear and precise proposals" from the UK government on breaking the Brexit deadlock, adding: "We are really exhausted by these negotiations."

He warned: "It's not just a game. It's an extremely serious situation, not just for the people in the UK but also for the people in the EU."

France's European affairs minister Nathalie Loiseau claimed the Commons needed to choose between leaving the EU without a withdrawal agreement or backing the prime minister's deal.

She noted how MPs "have said no to a 'no deal' and they have said no to a realistic deal" - adding: "They have to change their mind on one of the two options."

"If there is no decision, the date of 29 March comes and then it's a 'no deal.'

"For the British to decide nothing is to decide on a 'no deal'."

In order to prevent a no-deal Brexit, MPs have supported the prime minister asking the EU for an extension to the Article 50 negotiating period.

But, Ms Loiseau reiterated the EU's stance that there must be an "objective" behind any request for a delay to Brexit.

She said: "Grant an extension - what for? Time is not a solution, it's a method.

"If there is an objective and a strategy, it has to come from London."

The French politician added: "You have to have a sense of humour when you deal with Brexit right now."

Romania's European affairs minister, George Ciamba, whose country currently holds the rotating EU presidency, also called for "more clarity" from the UK over Brexit.

"The biggest issue right now is that it's getting more foggy," he said.