Downing Street has played down proposals from Boris Johnson that the UK could seek a Danish-style opt-out from European Union laws to allow it to control migration.
The Mayor of London said other leaders had given Britain the "bum's rush" by failing to agree to a ban on EU citizens from other countries claiming in-work benefits until they had been in the UK for four years.
Mr Johnson said Britain should be given a special settlement exempting it from certain EU rules, similar to that enjoyed by Denmark.
And he warned other EU leaders they were "radically and dangerously misreading" David Cameron if they believe the Prime Minister wants Britain to remain part of the 28-nation bloc at any price.
Britain's demands for reforms to the terms of its membership are on the agenda for a working dinner of EU leaders on Thursday, at the start of a two-day summit in Brussels.
Speculation is mounting that Mr Cameron may offer concessions over in-work benefits, after his proposal for a four-year ban was given a frosty reception by a number of leaders.
But Downing Street insisted that the plan remained on the table for this week's meeting, which is intended to pave the way for detailed negotiations between all 28 states ahead of an agreement which European Council President Donald Tusk hopes can be reached at the next summit in February.
"The Prime Minister is clear on the need to address the concerns of the British people ... about the level of migration from within the EU," said Mr Cameron's official spokeswoman.
"This is his proposal on the table and his position hasn't changed since he wrote to Donald Tusk last month setting out the areas where we need reform."
Mr Cameron had made clear he was "open to looking at" other ways of dealing with the issue, but insisted that any option adopted must deliver better control over EU migration to the UK, she said.
Writing in the Daily Telegraph, Mr Johnson warned other EU leaders that Mr Cameron was "much more Eurosceptic" than some other senior Tory figures and the UK must be offered reforms if the PM is to recommend continued membership in the in/out referendum promised by the end of 2017.
"The PM's suggestion was modest, and sensible. It has been recklessly disregarded," wrote Mr Johnson.
"If we are going to stay, we need reform; and if the Danes can have their special circumstances recognised, so can Britain."
But Downing Street said the Danish opt-out was on the "niche" issue of restrictions on second-home ownership, while Britain's proposals were more "significant and far-reaching" and were always expected to require extensive discussions among national leaders.
"What the Mayor of London has been setting out today highlights on the one hand that there is already flexibility within the EU, " said Mr Cameron's official spokeswoman.
"On the other hand, it is also a very specific and niche area where Denmark has some specific agreement, and that is linked to the purchase of second properties in Denmark, whereas clearly we are looking for something more significant and far-reaching in terms of benefits applying to workers from across the EU."
The spokeswoman said Mr Cameron was hoping this week's talks will "kick-start a process which can pave the way to agreement at the February Council".
But she stressed that Mr Cameron was not setting February as a deadline for agreement, adding that the process must be driven by the substance of reforms, and not by timetables.
In his regular Telegraph column, Mr Johnson wrote: "Waves of talent from overseas have helped to make our capital the most dynamic urban economy in Europe. But it should be up to us in this country to decide - as they do in America and Australia - whom to admit and when to admit them.
"Now our friends in Brussels have given us the bum's rush, and said that they won't agree to the four-year cooling off period that the PM has proposed. This would have meant that you can't come here and immediately clamp your jaws around the teat of the benefits system.
"I happen to think this idea would have been generally popular with European electorates, but never mind; they won't have it. So my question is: what will they agree to? We need to know.
"These people are radically and dangerously misreading the Prime Minister if they think he wants to stay in the EU at any price. The David Cameron I know is much more Eurosceptic than some of his senior colleagues.
"We need to hear soon about ways in which the British Parliament can halt the tide of EU regulation, and ways in which we can regain some control of our borders."