The Royal Air Force may not have permission from Parliament to conduct air strikes in Syria but pilots from Britain have already undertaken such missions, the Ministry of Defence has said.
The BBC said UK pilots embedded with coalition allied forces have conducted air strikes over Syria against Islamic State (Isis) targets.
"When embedded, UK personnel are effectively operating as foreign troops," the Ministry said.
Defence Secretary Michael Fallon had said previously that approval of MPs would be necessary before there will be any British military action in Syria.
In response to a Freedom of Information request by the human rights group Reprieve, the ministry has confirmed that some UK military personal have been involved in military action against IS over Syrian airspace, BBC reports.
"The MoD says those British military personnel embedded with US, Canadian and French forces and under their chain of command have been authorised to take part in those nations' operations. The US and Canada have been involved in air strikes over Syria," BBC defence correspondent Jonathan Beale said.
The UK has already been carrying out surveillance and air-to-air refuelling operations over Syria but has stopped short of air strikes.
In 2013, Labour voted against UK military action in Syria but has now indicated that it would not do so if the matter was put forward in parliament. MPs approved the bombing of militant positions in Iraq last year.
A MoD spokesman, referring to IS as Isil, said that the UK is contributing to the anti-IS coalition air campaign against IS targets in Syria through the provision of intelligence, surveillance and reconnaissance.
"IS poses a direct threat to the UK and to countries around the world. The UK is not conducting air strikes in Syria and the government has made it clear it would return to parliament if it proposed doing so."
"We have a long standing embed programme with allies but there are currently no pilots taking part in this region. When embedded, UK personnel are effectively operating as foreign troops."
NGO Reprieve said the debate on whether the UK should expand its military action to cover Syria is now obsolete and that the government should "come clean" about what its armed forces are already doing.