Boris Johnson's plan to have his Brexit deal passed on a Saturday sitting was scuppered by the passing of the Letwin amendment.

But what is the Letwin amendment and what impact will it have on Brexit?

What is the Letwin amendment?

The Lewtin amendment sought to withhold any approval of the prime minister’s deal until the withdrawal bill implementing Brexit has been passed. Under current plans, this could be up for a vote next week, with MPs expected to vote on Tuesday. 

With the Letwin amendment effectively cancelling any vote on Boris Johnson's deal on Saturday, it brought the so-called Benn Act back into play. The Benn act set a deadline of 11pm on Saturday for Johnson to win parliamentary approval of his Brexit deal, or request a delay. As a result, on Saturday night he sent an unsigned letter to the European council requesting a further Brexit delay beyond 31 October – accompanied by a signed one arguing against it.

The Letwin amendment was a way of trying to close a no-deal Brexit loophole. with its supporters fearing MPs could support the deal on Saturday, meeting the requirements of the Benn act, but then the legislation implementing Brexit could fall, allowing a no-deal exit on 31 October.

READ MORE: What is the Benn Act and will it have an impact on Brexit?

Does it extend Article 50? 

According to the terms of the Benn act, the government will have to request one – although Downing Street has in the past hinted it hoped to work around the legislation. It also does not rule out the EU27 could vetoing any request for a delay.

However, the legislation makes clear that if the government does pass the EU withdrawal bill before 31 October, then any extension would lapse. 

How did the amendment pass?

The majority of Labour, Liberal Democrat, Scottish National Party, Democratic Unionist party, Independent Group for Change, Plaid Cymru, and Green Party MPs and 17 other independents voted in favour of the Letwin amendment. 

As well as the official opposition backing the amendment, eleven of the 21 former Tories, who were kicked out of the party for trying to block no-deal, voted against it. 

Could Boris Johnson still get his deal through Parliament?

Yes, but time is running out before the October 31 deadline as the European Parliament would also need to ratify it, and it is unclear how soon MEPs will do that.

On Monday, the European Commission said the ratification process has been launched on the EU side.

But European Parliament’s chief Brexit official, Guy Verhofstadt, said last week MEPs will only start their work once the UK Parliament has passed a fully binding Brexit deal, and if that slips past the European plenary session this week, it may have to be picked up in the session that begins on November 13.

READ MORE: Scottish judges set to rule on whether Boris Johnson in contempt of court over Brexit letters 

And without a meaningful vote in Parliament, support for the agreement has not yet been tested.

Though the PM has attracted support from a number of prominent Brexiteer Tories, including the European Research Group (ERG), the DUP is strongly opposed to the deal.

What about the letters sent to the EU by Mr Johnson?

Under the terms of the Benn Act, which was passed against the PM’s wishes, the Prime Minister was compelled to write to the EU asking for a three-month Brexit extension if he had not secured a deal by 11pm UK time on October 19.

He told the Commons: “I will not negotiate a delay with the EU, and neither does the law compel me to do so.”

But the Prime Minister did send two letters to European Council president Donald Tusk.

First, there was an unsigned photocopy of the request he was obliged to send under the Benn Act, followed by a letter explaining why the Government did not actually want an extension.

Will there be an emergency EU summit?

If the PM gets the Withdrawal Agreement Bill through, there could be a special gathering of leaders on October 28.

If the deal needs more time at that stage to get through Parliament, leaders could agree to a short extension.