David Cameron and French president Francois Hollande tonight stepped up the campaign for the right to arm Syrian rebels after private talks in Brussels.
The Prime Minister and Mr Hollande got together at the latest EU summit to discuss their growing concern that an existing EU arms embargo against Syria is effectively preventing assistance to forces opposing the Assad regime's campaign of bombing and bloodshed.
EU sanctions against the Syrian regime, including an arms embargo, have only just been extended until the end of May - meaning only a unanimous vote of EU foreign ministers can change the situation before then.
And tomorrow - the second anniversary of the Daraa uprising against the Assad regime - the UK and French leaders will make a joint plea to fellow leaders to reconsider the arms embargo or face the prospect of at least two EU nations taking unilateral action to assist the rebels.
That would realistically only happen after the end of May, when the current sanctions are up once more for review. But the hope in London and Paris is that other member states will by then agree to end the sanctions early.
EU foreign ministers meeting in Brussels next week will take up this issue after tomorrow's summit discussions.
"There is a perversity about the EU arms embargo... it is backfiring" said one Downing Street official. "The embargo does not stop those aiding Assad, but it does stop those who want to help the opposition".
But the official emphasised: "We are not considering going ahead (with arming the rebels) while the current arms embargo is in place. What we want is to start the discussion about changing the arms embargo."
Mr Cameron has already hinted that "it's not out of the question we might have to do things in our own way".
And, arriving at the summit, Mr Hollande was forthright: "We are ready to support the rebels, so we are ready to go that far."
"We cannot allow the massacre of a people by a regime which right now does not want a political transition."
"France's view is that arms are being delivered to Syria - but to the regime of Bashar al-Assad, in particular by the Russians."
He said he was not looking for "total war", but for ways of increasing pressure on the Assad regime.
Earlier French foreign minister Laurent Fabius said the UK and France were ready to arm rebels in Syria, even without full EU support.
And UK Government sources had insisted that "all options" remain on the table.
Earlier a Foreign Office spokesman said: "Our objective is clear - an end to the violence and a political transition to a more democratic Syria through a political solution.
"As it stands, the political track has little chance of gathering momentum unless the regime feels compelled to come to the negotiating table. They need to feel that the balance on the ground has shifted against them.
"The Foreign Secretary has been clear he hasn't ruled out any options for the future."
A Downing Street official insisted tonight: "This is not about intervention in Syria by Western forces getting involved. It is about looking at what more can be done to support the opposition."