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MPs backed a rebel amendment this afternoon which has scuppered Boris Johnson's Brexit plan.
The Prime Minister wanted MPs to formally back his deal today but a proposal put forward by Sir Oliver Letwin to ruin the premier's hopes of making Brexit progress was passed by 322 votes to 306.
The amendment will now force the PM to ask the EU for a Brexit delay under the terms of the anti-No Deal law known as the Benn Act.
The amendment does not kill off Mr Johnson's deal and it will still be possible for him to deliver Brexit by October 31.
But the path to fulfilling his 'do or die' Halloween pledge will now be fraught with difficulty and the chances of a Brexit delay have increased exponentially.
Here is a breakdown of what is likely to happen now the amendment has been backed by MPs.
What happens if Boris Johnson does not send a letter to the EU asking for a Brexit delay?
The PM will now seemingly have to comply with the Benn Act and send a letter to Brussels asking for a Brexit extension.
The government has long maintained that it will comply with the law but Mr Johnson muddied the water immediately after the Letwin result was announced as he said he 'will not negotiate a delay with the EU and neither does the law compel me to do so'.
The Prime Minister's official spokesman then refused to answer questions about whether the PM will send the letter required by the Benn Act.
'We are not going to add anything to the PM's words in the House,' the spokesman said.
However, the spokesman did repeat that 'governments comply with the law' in a hint that the PM could send the letter while also potentially making clear to the EU that he does not want the bloc to grant a delay.
The PM has until midnight to comply with the terms of the anti-No Deal legislation.
Boris Johnson, pictured in the House of Commons today, wanted MPs to back his Brexit deal today but his plans were scuppered
The PM's hopes of making Brexit progress were torpedoed after an amendment put forward by Sir Oliver Lewtin was agreed by MPs. It is designed to force the PM to ask for a Brexit delay
Regardless of what happens with the letter, the PM is expected to bring forward the Withdrawal Agreement Bill - the legislation needed to actually make Brexit happen - on Monday this week to try to crash it through Parliament as quickly as possible.
If he is able to get MPs and peers to agree to the draft legislation in the coming days he would then be able to hold the 'meaningful vote' on his deal, paving the way for the UK to leave the EU on time.
What legal loophole does Boris Johnson think he has found?
The PM will have sought extensive legal advice on exactly what the Benn Act requires him to do.
Unless the government has come up with an unexpectedly brilliant and top secret legal argument against having to send the letter to the EU, it is hard to see how the premier can avoid asking the bloc for an extension.
However, it is possible Number 10 may well have concluded it can send the letter while also spelling out to the EU, potentially in a second letter or through other means, that the government does not actually want a delay in the hope one is not offered.
But such an approach will be closely scrutinised by Remain-backing MPs who will pounce if they believe the PM is trying to frustrate the purpose of the law.
Effectively, if the PM does anything to try to contradict the stated goal of the legislation - to ask for a delay - he could face accusations of trying to undermine the law.
What can Remainers do to stop the PM if he does not comply with the Benn Act?
If the PM fails to send the letter or is believed to have tried to frustrate the purpose of the Benn Act then Remainers will almost certainly launch immediate legal action and the battle over Brexit will head to the courts.
The turnaround on any legal challenge would likely be swift with a potential Supreme Court hearing in a matter of days.
What does the Benn Act actually ask the PM to do?
Contained within the legislation is a pre-written letter which the PM is required to sign and send to the president of the European Council, Donald Tusk, by the end of today if no Brexit deal has been agreed by MPs.
It asks the EU to postpone the Brexit divorce date until January 31 next year. The letter reads:
'The UK Parliament has passed the European Union (Withdrawal) (No. 2) Act 2019. Its provisions now require Her Majesty’s Government to seek an extension of the period provided under Article 50(3) of the Treaty on