The head of MI5 has warned that Britain continues to face a 'serious security challenge' - 10 years on from the 7/7 bombings in London.
52 people died in the terror attack, with more than 700 others injured.
Peter Clarke used to be head of the Metropolitan Police's counter-terror unit - and led an investigation into what happened on July the 7th 2005.
He agrees there is an ever-present risk.
