British Prime Minister Boris Johnson is to introduce legislation designed to prevent any further extension of the process of the UK's withdrawal from the European Union.
Downing Street said that when the draft of Mr Johnson's Brexit agreement is brought back to parliament this week, it will include a new clause saying trade talks cannot be taken beyond the end of December 2020.
Ministers are understood to have re-worked the Withdrawal Agreement Bill - due to come before the Commons this week - to "legally prohibit" any further extension.
Under current plans, the government intends to end Britain's EU membership on 31 January, with an implementation to run to the end of 2020 while it negotiates a free trade agreement with Brussels.
Tánaiste and Minister for Foreign Affairs Simon Coveney said Mr Johnson's decision to not delay the Brexit process past the end of next year would be "strange" for the EU.
Mr Coveney said it shows that Mr Johnson wants to move the process quickly.
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The post-Brexit transition period can currently be extended by mutual agreement for up to two years.
Mr Coveney said the new clause being pushed forward by Mr Johnson would ultimately close off options for Britain to seek more time if needed.
The Tánaiste is due to give Cabinet an update today on Brexit plans following the UK election last week.
The move by Mr Johnson comes as MPs gather at Westminster for the first sitting of the new Parliament following the election.
He addressed his new Cabinet, telling them "you ain't seen nothing yet folks".
He said: "The voters of this country have changed this government and our party for the better and we must repay their trust now by working flat out to change our country for the better."
He continued: "It was quite a seismic election but we need to repay their trust and work 24 hours a day, work flat out, to deliver on this.
"Of course, the first 100 days were very busy, 140 days or whatever it was, you may remember it was a very frenetic time but you ain't seen nothing yet folks.
"We are going to have to work even harder because people have a high level of expectation and we must deliver for them."
The Tories returned in buoyant mood after Mr Johnson was swept to an unexpected 80-seat majority as a swathe of Labour strongholds fell to the Tories.
Mr Johnson repeatedly promised during the election campaign that he would not seek any extension to the transition period.
The commitment was instrumental in persuading Nigel Farage not to stand Brexit Party candidates in Conservative held seats.
However, after Mr Johnson was returned with an unexpectedly large majority, there was speculation he could use his strengthened position to seek an extension if more time was needed to get a trade deal.
The latest move would appear to have put paid to that.
The Withdrawal Agreement Bill is due to be brought before the Commons on Friday and could receive its first reading and be voted on at second reading in one day, if the Speaker agrees.
Elsewhere, the Chair of the Seanad Brexit Committee has said the EU will meet Mr Johnson if he is "dead set on getting a trade deal done within ten months".
Speaking on RTÉ's Today with Sean O'Rourke, Neale Richmond said the British Prime Minister had been presented with a 'menu of options' from Michel Barnier.
Mr Richmond said that it was important that the British government outlined clearly what it wanted and what Brexit looks like to it.
Additional reporting Karen Creed
