David Cameron is examining the domestic impact of possible EU migration compromise deals as he faces a battle to persuade senior colleagues to support his renegotiation.
The Prime Minister wants EU workers to be barred from claiming in-work benefits for four years, but may have to accept the rules are also applied to UK citizens as the price of securing agreement from fellow leaders.
Downing Street indicated an option to require proof that an individual had been in the British labour market for four years was not under consideration after official analysis found that as many as 300,000 Britons could lose out.
"We are not considering any option that would affect this number of British citizens," a Number 10 spokesman said.
"The proposal on the table remains the one of limiting in-work benefits to EU migrants for four years with the aim of reducing the pull factors that have attracted such vast numbers of Europeans to the UK in recent years."
Around 50,000 home-grown workers would be affected if it was based instead on a residency test - but even that is reported to be opposed by some in the Cabinet, including Work and Pensions Secretary Iain Duncan Smith.
The Times said the PM held face-to-face talks with ministers including Northern Ireland Secretary Theresa Villiers and Justice Secretary Michael Gove in an attempt to maintain unity ahead of the in/out referendum, expected next year.
Mr Cameron faced renewed calls at the weekend to give Eurosceptic ministers the freedom to campaign for Britain to leave the EU amid warnings senior resignations were inevitable if he sought to enforce support for a "flimsy" deal.
He left last week's Brussels summit insisting he was "well on the way" to securing "fundamental change" to the relationship with Brussels at the next gathering in February and gave the clearest signal yet that he would lead the "in" campaign.
But former defence secretary Liam Fox declared that he would vote in favour of "Brexit" whatever new relationship the PM secured from fellow European leaders and urged Mr Cameron to "end the pretence".
And Steve Baker of the Conservatives For Britain group, said opinion in the party was "hardening" in favour of leaving.
Downing Street also rejected claims it was preparing a "Pro-EU dossier" to send to households ahead of the referendum.
The Telegraph said the document was supposed to set out "the changes, the benefits of the changes to Britain, and why therefore we need to stay in the EU".
A government spokesman said: "It is absolute nonsense to suggest the Government is working up a pro-EU pamphlet to send to families to discourage them from voting No in a referendum.
"What the Government is doing, as committed to in the EU Referendum Act, is producing public information on the outcome of renegotiation.
"We've always been clear that it is important that the British public are provided with the information they need to understand the consequences of their choice in the referendum."