British Foreign Minister William Hague met last week with members of the National Coalition of Syrian Revolutionary and Opposition Forces, an opposition council formed mid-November in Qatar.
The Turkish and French governments had already joined Arab political blocks in recognizing the legitimacy of the opposition council.
Hague said Tuesday that the British government has decided to recognize the council "as the sole legitimate representative of the Syrian people."
He said that, during last week's meetings, Syrian opposition leaders said their priority was assuring the safety of the Syrian people and viable political transition.
It would be for the people of Syria, they told me, to approve a future government," he said in a statement.
On the military front, Hague said he expected NATO leaders to assess the security needs of the Turkish government. NATO Secretary-General Anders Fogh Rasmussen ruled out a no-fly zone over Syria but said the Patriot missile system may be deployed along Turkey's borders for defensive purposes.
Italian Foreign Minister Giulio Terzi said he met with 26 Syrian activists in Rome. He said he was working with religious and civil groups to usher in a "democratic Syria, free from tyranny."
Washington said it welcomed the forming of the Syrian opposition council but has yet to recognize its legitimacy.