(CNN) -- The United Kingdom won't compromise over the sovereignty of Gibraltar in the latest row with Spain over the rocky outcropping on its southern tip.
"Our differences with Spain on Gibraltar will be resolved by political means through our relationship as EU partners, not through disproportionate measures such as the border delays we have seen over the past week," the UK Foreign Office said in a statement.
Spain recently ramped up border checks, leaving drivers languishing in line for hours on end. Spanish Foreign Minister Jose Garcia-Margallo also has suggested imposing a 50-euro fee on every vehicle entering and leaving Gibraltar.
A spokesman for British Prime Minister David Cameron called the prospect of fees worrisome. "Clearly, we remain seriously concerned by the events at the Spain/Gibraltar border on this issue of border fees. The Spanish have not raised the prospect of introducing border fees with us. We are seeking an explanation from them regarding reports that they might target Gibraltar with further measures."
Garcia-Margallo said the money would go to help fishermen whose fishing grounds have allegedly been damaged by authorities in Gibraltar. The British territory has been working on an artificial reef.
"We will be seeking an explanation from Spain following reports that the Spanish government might target Gibraltar with further measures," the Foreign Office said.
Britain's 300-year-long control of the Mediterranean colony has been a persistent irritant in its relations with Spain. Talks on its fate re-started in July 2001 after breaking off in 1987.
London and Madrid came close to a deal on joint sovereignty in 2002, but it collapsed after an unofficial referendum showing that 99% of Gibraltar's 30,000 residents opposed the change and feared they would be abandoned by Britain.
Britain gained possession of Gibraltar in 1704 and legal control of the strategic port with the Treaty of Utrecht nine years later. The treaty granted Spain the first right to reclaim Gibraltar if its status changed.