Prime Minister David Cameron said he wants to see al Qaeda-linked extremists "driven out" of Syria.
Mr Cameron acknowledged there are "deeply unsavoury" elements of the Syrian opposition that he wants "nothing to do with", but said the British Government would continue to offer non-lethal support to the "genuine" political opposition.
Speaking to Sky News' Murnaghan programme, the Prime Minister said: "There are elements of the Syrian opposition who want to see a free democratic, pluralistic Syria that respects the rights of minorities including Christians and we should be working with them - we are working with them.
"If we don't work with those elements of the Syrian opposition, then we can't be surprised if the only elements of the Syrian opposition that are getting, that are actually making any progress in Syria, are the ones that we don't approve of".
US President Barack Obama has tip-toed over the 'red-line' and armed Syrian rebels but it is a gamble of huge proportions.
Writing for ITV News, international affairs analyst David Butter looks at the timing of US support for Syria and when it may arrive.
Are the US supplied assault rifles too little, too late and what incentive is there for Assad to enter peace talks?