US, Britain and Canada carry out joint air strikes on Islamic State targets in Syria
British pilots have carried out military air strikes on Syria, the Ministry of Defence has revealed.
The UK personnel were embedded with the forces of allied nations, including the USA and Canada, which have been conducting strikes against the Islamic State (IS) terror group - also known as Isil or Isis.
The number of pilots involved was in single figures and none is currently taking part in air strikes.
The House of Commons voted against military action in Syria in 2013 and parliamentary authorisation has so far been given only to UK air strikes against IS in neighbouring Iraq.
But the MoD said any personnel embedded in foreign nations' forces were effectively operating as troops of that country.
British troops are regularly embedded in other nations' forces and have operated under US command since the 1950s, including in recent operations in Afghanistan, Iraq and Libya. The MoD agrees each deployment and continually monitors the permissions granted to embedded troops.
UK forces are taking part in surveillance and air-to-air refuelling operations over Syria, and in the wake of the murder of 30 Britons in a terror attack in Tunisia last month, David Cameron and Defence Secretary Michael Fallon made clear they are considering extending air strikes against IS into the country.
They have indicated that they would seek MPs' approval for an extension of air strikes into Syria, but no vote is expected before the autumn.
Details of British personnel's involvement in strikes by allied nations' forces were revealed by a Freedom of Information request from pressure group Reprieve.
A Ministry of Defence spokesman said: "When embedded, UK personnel are effectively operating as foreign troops.
"The UK is contributing to the anti-Isil coalition air campaign against Isil targets in Syria through the provision of intelligence, surveillance and reconnaissance.
"Isil poses a direct threat to the UK and to countries around the world. The UK is not conducting air strikes in Syria.
"But we 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.
"When embedded, UK personnel are effectively operating as foreign troops."
Mr Fallon said on Thursday that the UK was engaged in a "new Battle of Britain" against IS, as he confirmed the deployment of a second RAF Rivet Joint spy plane to the region.
Earlier this month, he said there was an "illogicality" about targeting IS in Iraq but not Syria, when the terror group did not respect international borders.
He suggested that the new Parliament may take a different view from its predecessor on strikes in Syria. Downing Street has said that more "thought and deliberation" are needed before putting the issue to a vote in the Commons.
Jennifer Gibson, staff attorney at Reprieve, said: "Documents obtained by Reprieve 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.
"Yet more worrying is the fact that the UK seems to have turned over its personnel to the US wholesale, without the slightest idea as to what they are actually doing, and whether it is legal.
"We need an open and honest debate about UK involvement in Iraq and Syria. We can't have that, though, until the UK comes clean about what actions its personnel are already undertaking."