British Foreign Secretary Jack Straw has admitted it would be difficult to go to war in Iraq without public backing.
But Mr Straw said he believed a majority would support conflict waged with a UN mandate.
A huge protest over the weekend, which saw nearly a million people take to the streets in London to oppose war in Iraq, has increased the pressure on the British government over its stance toward Baghdad.
Asked by a radio interviewer if Britain could go to war if a majority were opposed, Straw said: "It is very difficult indeed under those circumstances.
"It's patently more straightforward for governments to take a country to war, to military action, if they palpably have the public behind them than if not," he said.
"Yes, there was a very large demonstration, probably the largest we have seen in our recent democratic history in London on Saturday, and we have to take account of public opinion".
But he said parliament had backed the government's stance in a vote in November and the public was coming to understand that Iraq posed a threat.
Referring to public opinion polls, he said: "There would appear to be a majority for taking military action if that is endorsed by the United Nations, as we certainly want it to be."
Mr Straw said he "would not put a deadline" on efforts to draw up a new resolution and persuade sceptics such as France and Germany to approve force. But he said the international community must be prepared to apply force if needed.