The Foreign Secretary William Hague has put pressure on Spain over claims it is deliberately engineering lengthy delays at the border with Gibraltar.
In a telephone call with his Spanish counterpart, Garcia Margallo, Mr Hague raised "serious concerns" over severe delays caused when officials carried out intensive vehicle searches.
Thousands of cars leaving the British territory were stopped for checks causing six hour traffic jams in the searing heat.
Gibraltar's government accused Spain of "torture" by inflicting searches on vulnerable passengers and causing "unnecessary delays".
Mr Hague has used British diplomatic channels to make Britain's concerns of the dispute known over the weekend but tonight moved to intervene directly.
More top news
Islamic State poses as great a threat to Britain as the IRA during its bombing campaign in the 1970s, a watchdog has said.
Turning colder with showers in the west and windy for many, with severe gales in exposed northern and western parts.
The elderly woman's son complained to the council that his mother had been deprived of her liberty in an 'unprecedented' legal case.