The Labour leader has already confirmed Labour MPs will be whipped to vote in favour of the deal which was announced on Christmas Eve. It still needs to be ratified by MPs on Wednesday this week, with Parliament set to be recalled at 9:30am that morning to debate the Brexit legislation and give it effect.
Sir Keir has said MPs are faced with the choice of either the Brexit deal in front of them or no deal at all.
He added: “No deal would have terrible consequences for our country, and the Labour party could not enable that to happen.”
However, senior Labour MPs including former shadow chancellor John McDonnell have called the deal “rotten”.
Reports are saying there will be a ‘major’ rebellion from frontbench Labour MPs against Sir Keir’s position.
Despite the push, even MPs opposing the deal acknowledge it will pass through Parliament regardless given the Conservative Government’s majority.
In a statement, Labour rebels say they are aiming for “opposition” and “proper parliamentary scrutiny of this and all future trade deals”.
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Sir Keir has called the agreement “very, very thin” in certain areas but conceded Labour had made a “tough but necessary” decision to support it.
Other parties, such as Nicola Sturgeon’s Scottish National Party, have vowed to vote against the deal.
Ed Davey, leader of the Liberal Democrats, has not committed to vote against but has claimed Lib Dem MPs will “not be supporting it”.
There is less likely to be as significant an opposition to the deal within the Conservative party, The Guardian reports.
Tory Brexiteers are due to deliver their decision this afternoon following scrutiny of the deal’s details.
The deal has already been unanimously backed by EU member states – though the European Parliament has delayed its vote until sometime early in 2021.
Boris Johnson has said the deal “means a new stability and a new certainty in what has sometimes been a fractious and difficult relationship”.
He added: “I think that what we have got here is the basis of a new long-term friendship and partnership that basically stabilises the relationship.”