What is Spain v Gibraltar row about?
5 August 2013 Last updated at 23:13 BST
The Prime Minister says he has 'serious concerns' over Spanish proposals to charge a fee for crossing the border into Gibraltar.
Spain has said it is considering a range of proposals including a new 50 euro (£43) fee to cross the border into the British territory.
The chief minister of Gibraltar has accused Spain of sabre-rattling and "acting like North Korea" in the continuing dispute over fishing rights.
Tom Burridge reports.