Islamic State 'like air in a balloon', says Rusi's Michael Clarke

Islamic State (IS) militants have secured a significant victory in their battle against Iraqi forces, after taking the government compound in the strategically-important city of Ramadi.

Michael Clarke, director general of the Royal United Services Institute (Rusi), tells the BBC's Caroline Hawley that IS is "like the air in a balloon" - they may be squeezed out of one area but will reappear in another.