David Cameron is making key concessions on the EU Referendum Bill following pressure from Tory rebels and the SNP.
With a potentially embarrassing series of votes looming tonight, the Government has dropped the idea of holding the poll on the same day as elections in Scotland next May.
Movement is also expected on plans to scrap the "purdah" period running up to the in-out referendum, with ministers set to promise a "code of conduct" to ensure the Whitehall machine is not used to skew the vote.
The late shift came after whips seemingly realised they were on course for defeat on the matter of the date - with Labour, the SNP, some Conservative backbenchers, and the DUP joining forces to oppose doubling up with elections.
A senior government source said: "We've listened to the views expressed from MPs across the House and agreed that we won't hold the referendum on the same day as legislature elections."
SNP foreign affairs spokesman Alex Salmond said ministers tabled their own amendment only when it became evident they faced "retreat or defeat".
"It was clear that the Tories were angling to hijack Scottish elections with the EU referendum and the united opposition have blown them off course," he said.
"This is very much the shape of things to come and has hopefully taught this arrogant Tory government to cease their disrespect towards the nations of Scotland and Wales and the people of Northern Ireland."
Conservative Eurosceptics have tabled amendments to the Bill that would reinstate the standard 28-day purdah restrictions laid down by the Political Parties, Elections and Referendums Act 2000.
However, Downing Street has been arguing that the rule will cause particular problems in this case because of the volume of day-to-day government business which involves the EU, and the need for the Prime Minister to make Commons statements on European issues.
Efforts have been ongoing to hammer out a purdah "framework" that will satisfy concerns on both sides, and ministers are expected to pledge a "code of conduct".
However, it is unclear whether the concession will be enough to assuage the rebels. Former environment secretary Owen Paterson - one of the ringleaders - said last night that he was still "hoping for a rethink".
The Government's position has been strengthened after Labour indicated that its MPs will be ordered to abstain in the key vote - significantly reducing the chances of defeat.
Tory Eurosceptic Bernard Jenkin said the rebels would not back down over calls to reinstate the purdah period.
He told the BBC Radio 4 Today programme: "I think the Government has been very badly advised, obviously on the date and on this. If they had accepted the Electoral Commission's advice on purdah we wouldn't be in this mess."
He warned that people will think the Government is "trying to rig" the referendum unless there was a purdah period.
Mr Jenkin added: "It's about fairness and trust. Who will trust the result of this referendum if the Government have been able to deploy their vast resources pushing propaganda through people's letterboxes?
"It's about journalists ringing up civil servants and saying 'What does the Government mean by this?' and, instead of saying, as during a general election, 'I'm sorry that's a matter for the No campaign or the Yes campaign' the Government uses its entire publicity machine to brief the media, to skew the battlefield in favour of their particular side of the debate.
"I don't think anybody in their right mind wants this. I don't think the Government wants it. I think they realise they have opened a bit of a Pandora's box. They will be looking for a way to resolve this.
"But the bottom line is they should restore purdah in this Referendum Bill and, if they want to bring forward amendments later in the Bill to deal with particular concerns they have got, let's talk about that.
"But we can't back down on this amendment."
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