The stakes rise as European leaders prepare to meet...
Downing Street said the two leaders agreed in Paris that the proposals on Britain's relationship with Europe provide a "firm basis" for reaching an agreement later this week.
However, the Paris meeting came after EU Council president Donald Tusk said the talks on reforming the bloc are at a "critical" stage and there is a "real risk" that the EU could break up.
This is a critical moment. Risk of break-up is real as #UKinEU negotiations very fragile. Handle with care. What is broken cannot be mended— Donald Tusk (@eucopresident) February 15, 2016
After negotiations in Romania, Mr Tusk said: "It will be a crucial summit with the two biggest challenges to the future of the European Union on the agenda: The United Kingdom's future membership of the European Union and the migration crisis.
"On neither can we afford to fail.
"At stake is the United Kingdom's membership of the EU. A question which only the British people can and will decide.
"At stake is also the future of our European Union where we will all have to decide together, and where we cannot and will not compromise on the fundamental freedoms and values."
He added: "This is a critical moment.
"It is high time we started listening to each other's arguments more than to our own.
"The risk of break-up is real because this process is indeed very fragile. Handle with care. What is broken cannot be mended."
Mr Cameron is due to meet European Parliament president Martin Schulz and three MEPs who have been appointed "sherpas" for the renegotiations.
He will then meet leaders of the Socialist and EPP groupings - but not UKIP leader Nigel Farage.
As Leader of the party that won the European Elections, @David_Cameron is insulting millions of British people by refusing to meet me.— Nigel Farage (@Nigel_Farage) February 15, 2016
Mr Farage said a planned meeting had been cancelled at the last minute and tweeted: "As leader of the party that won the European Elections, David Cameron is insulting millions of British people by refusing to meet me."
The politician tweeted his concerns after the latest in a series of meetings across the continent to win support for his proposals.
The draft text, based on reforms that David Cameron wants to achieve, is to be discussed by 28 EU leaders at a summit on Thursday.
Sky News reports that Mr Cameron has agreed to hold an emergency Cabinet meeting on Friday if he secures an EU deal at the Brussels summit.
The British PM has offered to talk to any Cabinet colleagues who may have questions over his EU renegotiation efforts.
Several ministers are understood to have reservations.
The meeting will see the suspension of "collective responsibility", so members of the Cabinet will be free to express their views and support either the "leave" or "remain" campaigns in a referendum on Britain's membership of the EU likely to take place in June.