American generals asked Britain to boost its troop contingent to the international coalition as commanders hope to capitalise on momentum which has seen Islamic State in Iraq and Levant (Isil), also known as Daesh, lose large parts of its self-style caliphate in recent months.

Mr Fallon said: "Iraqi forces have Daesh on the back foot and are retaking territory, hitting its finances and striking its leadership.

"This deployment will help the Iraqi forces to build on this success and push them back further.”

The new trainers will be stationed alongside US and Danish troops at Al Asad Airbase in Western Iraq, teaching the Iraqi Army 7th Division, border guards and federal police basic infantry skills, first aid and how to deal with homemade bombs.

The UK reinforcements also include 90 personnel to help guard the airbase, and around 30 headquarters staff. The engineers will spend six months building infrastructure.