Six hour tailbacks hit the Spanish/Gibraltar border after Spanish police stopped thousands of vehicles causing "deliberate" delays.
On Friday and Saturday, Spanish customs officers stopped thousands of vehicles trying to leave the territory for Spain. On Sunday the delays switched to traffic trying to enter Gibraltar.
Officers from the Royal Gibraltar Police were forced to impose diversions and create beachside holding areas due to the queues.
Gibraltar says Spain has created "deliberate" delays for vehicles travelling to and from the British territory.
The UK government has raised "serious concerns" with Spain about the border delays caused by a rise in vehicle searches, the BBC reports.
Gibraltar said the delays were "linked" to an artificial reef created to block fishing in a dispute over fishing rights between the two countries.
The sovereignty of Gibraltar is a major source of tension between the UK and Spain but both in 1967 and 2002, the people of Gibraltar rejected proposals for Spanish sovereignty.
