RAF Reaper drones will fly surveillance missions over Syria, the UK's Defence Secretary has announced.

The missions will start in a matter of days but the drones will not be authorised to fire on targets.

The RAF Rivet Joint spy plane will also expand its area of operations into Syria.

Michael Fallon told MPs in a written statement: "As well as their operations over Iraq, both Reapers and Rivet Joint surveillance aircraft will be authorised to fly surveillance missions over Syria to gather intelligence as part of our efforts to protect our national security from the terrorist threat emanating from there.

"Reapers are not authorised to use weapons in Syria; that would require further permission."

Britain has 10 Reaper drones.

They have been based at Kandahar airbase in Afghanistan but controlled by pilots based at RAF Waddington in Lincolnshire. It is understood they will be moved to an airbase in Kuwait.

They are armed with Hellfire missiles and do have permission to fire at Islamic State forces in Iraq.

The British Government insists strike missions in Syria can only be carried out with Parliamentary approval but the latest development will encourage accusations of mission-creep.

A Number 10 spokeswoman said: "We are using these assets to enhance our capability to gather intelligence and protect Britain from threats emanating from Syria.

"The Prime Minister and Government have made clear that we would return to Parliament for a separate decision if we were proposing to take military action. This is about intelligence gathering.

"We've also made clear that, if there was a critical national interest at stake or we needed to act swiftly to prevent a humanitarian catastrophe, we would act immediately and explain to Parliament afterwards. I think our approach is consistent with that."