Theresa May will reportedly begin Brexit on Thursday morning when The Queen signs Article 50 into law.
The Prime Minister told MPs on Tuesday that royal assent was expected within the "coming days" and promised to come to the Commons later this month to announce when she had triggered Article 50.
Government sources indicated that royal assent was expected at 11am on Thursday.
It will then be open to the Prime Minister to notify Brussels that the UK is leaving the EU, starting the two-year countdown to Brexit.
Mrs May has said she will invoke Article 50, the legal mechanism for withdrawal, by the end of the month.
The European Union (Notification of Withdrawal) Bill was passed by MPs and peers on Monday, with royal assent the final stage in the process.
The move comes after ministers were accused of "driving towards a cliff-edge with a blindfold on", as Brexit Secretary David Davis admitted they have made no assessment of the economic implications of failure to secure a deal with the rest of the EU.
The Prime Minister has declared her readiness to walk away from Brexit negotiations without agreement, insisting that "no deal is better than a bad deal".
And Foreign Secretary Boris Johnson said in a TV interview at the weekend it would be "perfectly okay" to crash out of the EU on World Trade Organisation (WTO) terms.
European Council president Donald Tusk said the signals coming from the UK Government just weeks ahead of the start of negotiations amounted to "threats", but insisted Brussels would not be "intimidated".
Failure to reach agreement on a future UK-EU relationship would be worse for Britain than for the remaining 27 states, he told the European Parliament.
Mr Davis tried to ease tensions with Brussels, urging colleagues to ensure future comments about the upcoming negotiations are "as calm as possible and as amicable as possible".
He issued a barely-veiled swipe at Mr Johnson, telling MPs on the Commons Exiting the EU Committee that he was preparing his strategy on the basis of "facts... not throwaway lines in interviews".
But he was unable to provide the committee with an estimate of the cost of "no deal", and said it might be a year before he could offer any figures.
Mrs May's "no deal is better than a bad deal" mantra was coined "in the emotional aftermath of the referendum (when) there were lots of threats of punishment deals", said Mr Davis.
"We had to be clear that we could actually manage this in such a way as to be better than a bad deal, and that is true.
"I can't quantify it for you yet. I may well be able to do so in a year's time.
"It's not as frightening as some people think, but it's not as simple as some people think."
Shadow Brexit secretary Sir Keir Starmer accused the Government of "recklessly talking up the idea of crashing out of the EU with no deal" while making no assessment of its potential cost.
Liberal Democrat Brexit committee member Alistair Carmichael said the Government's approach was "the equivalent of driving towards a cliff-edge with a blindfold on".
Mr Davis insisted a good Brexit deal was "eminently achievable" and said his impression from speaking to ministers from the remaining 27 member states was that "there is a growing determination to get a constructive outcome".