Bank of England chief Mark Carney has warned that "less than half of businesses" are ready for a no-deal Brexit as he appealed for a transition deal to be agreed.
The Governor of the Bank was speaking after he released analysis suggesting the UK would be tipped into a recession worse than the 2008 financial crisis if it exited the EU with no agreement in place.
He told BBC Radio 4's Today programme: "We know from our contacts with business, others know from their contacts, that less than half of the business in the country have initiated their contingency plans for a no-deal Brexit.
"All the industries, all the infrastructure of the country, are they all ready at this point in time? As far as we can tell, the answer is no."
Mr Carney also hit back at those who accused the Bank of scaremongering after it said no deal would result in an 8% cut in GDP, unemployment surging to as much as 7.5% and house prices falling by almost a third.
He said: "We have a responsibility to have systems ready for whatever happens."
Asked what type of Brexit he would like to see, Mr Carney said he did not have a preference, other than to see a transition period agreed.
"From a financial system perspective, something in the 18 to 24 months is sufficient," he said.
"For the economy as a whole, and in terms of putting in place the customs arrangements of the future, the question is - are those all in place? And the answer is no."
His comments come as Theresa May faces a grilling from senior MPs over her controversial Brexit agenda at the Commons Liaison Committee.
But she has been boosted by strong backing for her Withdrawal Agreement from a prominent Cabinet Leave supporter.
Commons Leader Andrea Leadsom backed the PM's stance in a letter to constituents, according to the Daily Mail.
She said it had been a "challenging journey", but Mrs May's plan was the only deal on the table, which meant the UK would quit the bloc in March, the newspaper said.
But DUP leader Arlene Foster reiterated that her party's 10 MPs would not support the Withdrawal Agreement when it comes to Parliament, saying it would create a "huge democratic deficit" in Northern Ireland.
She said: "All the things that made us vote for Brexit are the things that are going to be imposed on Northern Ireland."
Ms Foster also hinted that if the deal fails to get through the Commons, her party could be open to a so-called "Norway-plus" arrangement, where the whole of the UK stays in the customs union.
She told the same programme the DUP's "one red line" is to make sure Northern Ireland is not differentiated from the rest of the UK in terms of customs and is "not prescriptive" about other potential options on the future relationship with the EU.
Her comments came as the Government confirmed MPs will debate the Brexit deal eight hours a day for five days leading up to a crunch vote on December 11.
MPs will be allowed to vote on six amendments to the Government motion backing the deal during the Commons showdown.
Commons Speaker John Bercow will decide which amendments are debated and decided on by MPs ahead of the so-called "meaningful vote" on Government proposals.
Labour leader Jeremy Corbyn said his party could not back Mrs May's plan as it failed to ensure participation in a "strong" single market and customs union.
The move came as Labour said a new referendum would be inevitable if Mrs May's plans are voted down.
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