Gibraltar's chief minister Fabian Picardo will meet with David Cameron in Downing Street today as the problems on Gibraltar's border with Spain continue.
Ahead of the that meeting, police in the British territory are now investigating claims that Spanish border guards had missiles thrown at them by motorists angry at long queues to exit the peninsula.
Officers of the Guardia Civil are said to have passed an unofficial report to Royal Gibraltar Police officers after the incident and an investigation is now under way.
The small number of missiles were alleged to have been thrown from the motorcycle lane at rush hour last night when many workers were trying leave Gibraltar to return to Spain.
With queues to leave Gibraltar running to around four hours, some commuters were also said to have shouted insults and abusive comments at the Spanish border guards.
There have been long queues at the border in recent weeks after a deterioration in relations between the UK and Spain over Gibraltar.
The Spanish have protested to the British government after Gibraltar created a reef in waters just off the coast, apparently to protect fish stocks. The Spanish argue the man-made reef compromises the ability of their fishermen to make a living.
As a result, Spain has toughened checks on the border, slowing traffic and threatening to impose a 50 euro fee for crossing from one country to the other.
Many in Gibraltar believe the row is being used by the Spanish government to deflect attention from a party-funding scandal back home.
Mr Picardo met the Foreign Secretary William Hague yesterday as part of efforts to resolve the dispute.