The Ministry of Defence released the information
in response to a request from human rights group Reprieve.
"The UK itself is not conducting air strikes in Syria," a Ministry of Defence statement said.
"But we do have a long-standing embed programme with allies, where small numbers of UK personnel act under the command of host nations. That has been the case in Syria, although there are currently no pilots operating in this region."
The ministry added that "when embedded, UK personnel are effectively operating as foreign troops" and are subject to the mandate of that government.
UK troops have been embedded with French, Canadian and U.S. forces, of which only the latter two have been conducting sorties in Syria.
In 2013, lawmakers in the House of Commons rebuffed Prime Minister David Cameron's call for a strong response to allegations the Syrian government had used chemical weapons.
Parliamentary authorization has only been given for UK military action in neighboring Iraq
as part of the international coalition against ISIS.
UK forces have been "contributing" to the coalition mission against ISIS in Syria "through the provision of intelligence, surveillance and reconnaissance," the Ministry of Defence said.
The revelation that some embedded pilots have taken part in airstrikes in Syria comes at a time when the question of whether UK forces should be involved there has again been raised.
Jennifer Gibson, staff attorney at Reprieve, said the documents obtained by the rights group "indicate that UK personnel have already been involved in bombing missions over Syria for some time -- making the current debate over whether Britain should carry out such strikes somewhat obsolete."
"It is alarming that Parliament and the public have been kept in the dark about this for so long."
Gibson called for "an open and honest debate about UK involvement in Iraq and Syria," but said that before that could happen, the United Kingdom must come clean about what its personnel already is doing.