David Cameron has accepted that he will not get agreement on his EU renegotiation at this month's Brussels summit.
The Prime Minister has told German chancellor Angela Merkel that the scale of his demands meant it would not be possible to get an agreement "in one go".
In a telephone call with the German leader, he said that he hoped to use their final gathering this year to "keep up the pace of discussions".
"The Prime Minister explained that his priority is to get the substance right, underlining the need for legally binding, irreversible changes," a No 10 spokesman said.
"He noted that the scale of what we are asking for means we will not resolve this in one go and consequently he did not expect to get agreement at the December European Council.
"Instead, we should keep up the pace of discussions and use the summit for a substantive discussion of the proposed changes in each area."