The boost to the National Coalition headed by Ahmad Jarba comes 10 days after the United States extended similar recognition to the umbrella group.
After a meeting of the Friends of Syria group in London, Hague said Britain would provide an extra 50 million USD, 37 million euros in "practical support to help the opposition" against Syrian President Bashar al-Assad.
"We have also decided to upgrade the status of the National Coalition's representative office here in London to a mission in recognition of the strength of our partnership," Hague said.