PA MEDIA
The post-Brexit transition period - due to conclude in December 2020 - can currently be extended by mutual agreement for up to two years.
But an amended Withdrawal Agreement Bill the Commons is set to vote on this week would rule out any extension.
The PM told MPs it would put an end to years of "deadlock, dither and delay".
As the House of Commons assembled for the first time since the election, Boris Johnson said his priority was to "get Brexit done". He also promised to seek "common ground" and to approach politics with a "new and generous spirit" after the rancour of recent years.
Jeremy Corbyn congratulated the Conservative leader on his victory but said he would be "judged" on whether he delivered on the "many, many promises" he had made during the campaign, including to longstanding Labour voters.
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The UK is set to leave the EU on 31 January, more than three and a half years after the public backed Brexit in a referendum.
Soon after, the two sides will begin talking about their future economic relationship, including controversial areas such as fishing rights, consumer and environmental standards and financial services.
Trade deals typically take many years to conclude and senior EU figures are sceptical that a deal can be agreed within that time. If it is not, the economic relationship will default to World Trade Organization (WTO) terms, with the likelihood of tariffs on imports and exports.
The EU's chief negotiator Michel Barnier said the bloc would "do the maximum" to finalise the deal in time. Asked about the UK's refusal to contemplate any extra time for the talks, he said "it is the British choice to choose the procedure it wants".
Political signal
This is a political signal, a moment of early chest beating too, designed to disappoint those who might have been hoping No 10 might slide to a softer Brexit over the next few months.
And designed to gratify those who are adamant that Brexit must be completely "done" as soon as possible.
Boris Johnson seems to have concluded that if the talks are to go anywhere fast, there has to be a convincing clear deadline.
It was his vow of a Halloween deadline that got him to Downing Street in the first place, and although it was broken in the end, there's little question that his attitude towards extending again and again changed the dynamics of the talks with the EU that got the revised deal done.
Putting the deadline into law may also be designed to focus minds in Brussels. How effective that might be? That's a different question.
Shadow Brexit secretary Sir Keir Starmer said the PM's move was "reckless and irresponsible" and he argued that Mr Johnson was "prepared to put people's jobs at risk".
Liberal Democrat interim leader Sir Ed Davey said: "The only way Johnson can meet the December 2020 timetable is by giving up all his previous promises to Leave voters and agreeing to all the demands of the EU."
Downing Street has said the government plans to ask the new Parliament to have its first debate and vote on the withdrawal agreement - the legislation needed to ratify Brexit - on Friday.
With a majority of 80 following Thursday's general election, Mr Johnson is expected to get the bill into law with few changes in time for the UK to end its EU membership on 31 January.
So, the government is going to pass a law to stop itself doing something that it had already promised not to do.
On the surface, that doesn't change much.
Because the decision on whether to extend the transition period lies with the prime minister anyway, not with Parliament.
And with his new majority, Mr Johnson knows his critics can't do anything to force his hand.
But as a statement of intent, this announcement is important.
By reaffirming Mr Johnson's guarantee that the transition period will not be extended, it suggests there will only be enough time to agree a pretty basic trade deal which would leave many important issues unresolved.
That means a quick 'zero tariffs zero quotas' deal on goods could be done, as long as the UK is prepared to sign up to the EU's main conditions.
They include the UK sticking with EU rules on environmental and social policy, and on state aid for companies.
Such an agreement wouldn't get rid of all border checks, though, and it wouldn't do anything for the services sector.
The PM could of course change his mind again - he's done that before.
But this is also a warning for businesses - they could be in for a bit of a bumpy ride at the end of next year.
As well as ruling out an extension, the Independent reports that the amended withdrawal agreement may omit previous "provisions to ensure that workers' rights were not weakened after Brexit".
Cabinet minister Michael Gove said workers' rights would be "safeguarded" in separate legislation, adding that the government wanted to make sure the Withdrawal Agreement Bill passes through Parliament "cleanly and clearly".
But shadow chancellor John McDonnell said the government would "sacrifice our basic rights and certainty for business at the altar of turning the UK into a Trump-supporting tax haven".
And Labour's Barry Gardiner said his party would be less likely to support the bill if clauses on workers' rights and the environment were removed.
The prime minister promised during the general election campaign that he would not seek an extension to the transition period - persuading Brexit Party leader Nigel Farage to stand down candidates in Tory seats.
Sam Lowe, from the Centre for European Reform think tank, told BBC Radio 4's Today programme that a December 2020 deadline could help the PM manage his own party when it comes to making concessions to the EU.
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"The prospect of a no-deal is still there," Mr Lowe said. "The question is whether Boris Johnson wants a no-deal but the evidence of recent time suggests no he doesn't."
Meanwhile, in the first act of the new Parliament, MPs re-confirmed Commons Speaker Lindsay Hoyle in his post without any opposition.
The MP for Chorley, who was only succeeded John Bercow at the start of November, said it was the "greatest privilege" to be asked to take the chair again and he would do his utmost to "cherish the best traditions" of the Parliament.
Commons officials have begun the process of swearing in the new MPs - which will continue on Wednesday.
What will happen this week?
Tuesday and Wednesday
After the election of the Speaker, the process of swearing in MPs begins. They are required to take an oath of allegiance to the Crown, or, if they object to this, a solemn affirmation. Those who speak or vote without having done so are deprived of their seat "as if they were dead" under the Parliamentary Oaths Act of 1866.
Two to three days are usually set aside for this process.
Thursday
The state opening of Parliament. The Queen's Speech is the centrepiece of this, when she will read a speech written by ministers setting out the government's programme of legislation for the parliamentary session. A couple of hours after the speech is delivered, MPs will begin debating its contents - a process which usually takes days.
Friday
Depending on how rapidly Boris Johnson wants to move, the debate on the Queen's Speech could continue into Friday.
The government will introduce the Withdrawal Agreement Bill to Parliament.
MPs in the previous Parliament backed Mr Johnson's bill at its first stage but rejected his plan to fast-track the legislation through Parliament in three days in order to leave the EU by the then Brexit deadline of 31 October.
After the debate on the Queen's Speech is concluded, MPs will vote on whether to approve it. Not since 1924 has a government's Queen Speech been defeated.
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