UK Foreign Secretary Philip Hammond's visit to Saudi Arabia comes at a time of strained bilateral relations, with the British government cancelling a Saudi prisons contract amid criticism of the Gulf state's human rights record.

The Saudi ambassador in London has threatened "potentially serious repercussions" unless a more respectful discourse is developed, pointing out that his country is one of the UK's closest military allies in the Middle East and an important trade partner.

So why does Saudi Arabia matter so much? BBC News explains its significance - in 60 seconds.

Video produced by Mohamed Madi