Syrian opposition groups were urged to develop a "common platform" by Foreign Secretary William Hague when they met him for talks in London.
More than 3,500 Syrians have been killed in a brutal crackdown since the start of a popular uprising against president Bashar al-Assad's regime in March, the United Nations believes.
But the UK has not felt able to grant formal recognition as it did to Libyan rebel forces because there is not a single, unified movement against the regime.
Speaking after the meetings, Mr Hague said: "I urged Syrian opposition groups today to come together peacefully and agree a common platform for the future of Syria.
"At an extreme moment in their nation's history, it is important for opposition groups to be able to put aside their own differences and come to a united view of the way forward."
There are fears that the country could descend into civil war if the regime is toppled without a cohesive alternative opposition to fill the vacuum.
One element is the Free Syrian Army, which claims to have recruited 15,000 dissidents from the regular forces but is controversial with protesters wanting a peaceful uprising.
Mr Hague emphasised "the importance of retaining international support in this situation through non-violent protest" and the need to respect minority interests in any transition.
He has appointed an "ambassador-designate" to lead liaison efforts. The groups also met with Downing Street officials ahead of the talks with Mr Hague.
The Foreign Secretary earlier expressed hope that further international pressure would be exerted on the "appalling and unacceptable" government in Damascus.
Removing the regime remained "the best thing for Syria", he said.
At the same time however, Russia accused western nations of undermining peace efforts by discouraging opposition groups from seeking a compromise with president Assad.
Foreign minister Sergei Lavrov said resistance forces shared responsibility for the carnage and should be under equal diplomatic pressure to end violence and enter talks.
Failing to encourage dialogue was "political provocation on an international scale", he said.