Britain has recognised a new coalition of Syrian opposition groups as the sole legitimate representative of the Syrian people.
The Gulf states, Turkey and France have already recognised the National Coalition for Syrian Revolutionary and Opposition Forces, although the United States has stopped short of doing so.
Foreign Secretary William Hague said the formation of the group was a major breakthrough and London will provide increased support to it.
He said they were now a "credible" alternative to the Assad government.
Mr Hague said the opposition would be given £1.6 million to help with communications equipment and assistance to set up political and humanitarian structures.