Former Foreign Secretary David Miliband has told ITV News that Britain could take around 25,000 refugees during the current crisis.
Mr Miliband said there could not be a limitless number but the scale of the crisis "demands" Britain take "tens of thousands" of people needing help.
"This has now become not just a political crisis and a policy crisis, but a moral crisis," he told ITV.
"I think it's very clear that the scale of the crisis demands that countries like Britain do take tens of thousands."
Mr Miliband, head of the International Rescue Committee, said it was "the time for action now".
He said the absence of "legal and efficient" routes for people to claim refugee status had empowered criminal gangs.
Speaking from New York, he described Germany's pledge to take 800,000 refugees as "extraordinary" but said countries including Britain, the United States and Gulf states needed to help.
"The Prime Minister is right to say that stability in the region is essential, including humanitarian aid, but Europe has to clear up its own mess now," Mr Miliband said.
He said it is time for "much more political and diplomatic muscle" to deal with the crisis.