Ministers are on a collision course with Tory rebels after refusing to back down over plans to drop purdah rules for the EU referendum campaign.
In a letter to Conservative MPs ahead of a crunch Commons vote, Europe minister David Lidington stressed he was ready to "engage" with those who had strong feelings on the issue and bring forward amendments to the legislation at a later date.
But he reiterated that it would be "unworkable and inappropriate" to impose the standard 28-day period in which Whitehall cannot get involved in debate.
"Working out a system that will reassure colleagues and voters that the referendum is a fair fight, yet will preserve the Government's ability to act in the national interest is not straightforward. It is important that it is legally clear and robust," Mr Lidington wrote.
"Therefore, we will work with colleagues over the next few months to understand their specific areas of concern and bring forward at report stage in the Autumn government amendments that command the widest possible support within the House and put beyond any doubt that the campaign will be conducted throughout in a manner that all sides will see as fair."
The message was immediately rejected by Tory rebels, who said they would still push the matter to a vote in the House.
"This is a very simple issue of principle," Bernard Jenkin told the BBC's Daily Politics. "If they do not accept the amendment we will push it to a vote."
Another rebel ringleader, Owen Paterson, said: "We need proper purdah."
A significant rebellion would be highly embarrassing for David Cameron just six weeks after his general election victory. However, the chances of the government being defeated has reduced after Labour indicated it is likely to abstain in any purdah vote.
Mr Cameron already made one concession last night by dropping the idea of holding the referendum on the same day as elections in Scotland next May.
A government amendment was hurriedly tabled after whips seemingly realised they were on course for defeat - with Labour, the SNP, some Conservative backbenchers, and the DUP joining forces to oppose combining the polls.
Conservative eurosceptics have tabled amendments to the EU Referendum Bill that would reinstate the standard 28-day purdah restrictions laid down by the Political Parties, Elections and Referendums Act 2000.
Downing Street has been arguing that the rule will cause 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.
There have been indications that ministers will propose a "code of conduct" to provide reassurance that they will not abuse the lack of a formal purdah period.
The proposals put forward by Mr Lidington were discussed at the weekly meeting of Cabinet at 10 Downing Street.
Mr Cameron's official spokeswoman said Mr Lidington told the Commons last week that he had heard MPs' concerns and would provide credible assurances on the framework for the referendum vote.
"Our approach is we want to listen and work on this, but we need some time to make sure we get it right," she said.
"The Prime Minister's absolute priority in this is to give the British people their say. That's what counts for people out there - they want to have their say on whether the UK should stay in the EU or not.
"What you see in the way we are approaching this at committee stage is us seeking to listen to views expressed across the House and look at how we might respond to those."
Asked whether Mr Cameron was hoping that backbench amendments would now be withdrawn, the spokeswoman said: "We have set out what we think a way forward is, which is for the Government to go away and do more work on this and come back to it at report stage. We have set out what we think the Government would like the way forward to be."
The spokeswoman made clear that the Government's amendment on the timing of the referendum applied only to the specific date of May 5 2016 - leaving open the possibility that it could be staged on the date of council elections in England and Scotland in May 2017.
She said it was too early to say whether taxpayer-funded resources would be used before the start of the official 28-day referendum campaign to publicise the Government's view on the merits of continued EU membership.
"That's a decision for later on. First we need to have a renegotiation and achieve the reforms that the PM is seeking to address the concerns of the British people," she said.
"The debate has been about what we would do in the last four weeks and that's where we have been clear that we won't spend public money to deliver mailshots."
The spokeswoman indicated that the Government has not ruled out Labour's proposal for a list of publications and announcements to be permitted during the purdah period.
"There are a number of ways you might seek to do it. I'm not ruling (any) in or out," she said. "The point is we need to take time to work out the right system."
And she added: "Our view is that it would be inappropriate to be fully applying the restrictions as they are set out in Section 125 of the 2000 Act in this instance. That's why we've sought to lift them, and now we have to find a way forward that balances giving the flexibility for the Government to publish while addressing people's concerns."