UK considers legal action against Spain over Gibraltar checks Motorists queue at a border crossing Britain denounced Spain's border checks on people entering Gibraltar as "politically motivated and totally disproportionate" on Monday as Downing Street warned Madrid it was "seriously considering" legal action over the dispute. David Cameron is expected to take a decision within days over what action to take after his appeal to Mariano Rajoy, his Spanish counterpart, last week failed to ease diplomatic tensions. The UK could ask the European Commission to intervene against Spain on its behalf or could instead choose to take direct legal action against Madrid. "Our preference is to de-escalate but we are not waiting for that to happen before outlining future steps," said a Downing Street aide. We don't want to damage relations but these delays are unacceptable. Spain was defiant in the face of British threats, insisting that its border controls - which have caused long delays for people entering the disputed UK territory - were a legitimate part of efforts to combat smuggling. Tensions first flared up earlier this month over fishing rights in Gibraltar waters. Officials have cited several recent examples of interceptions of illegal tobacco, including €11,000 worth of cigarettes seized from a car at the border last week. Spain said it was considering teaming up with Argentina to launch a joint diplomatic offensive against the UK through the UN in a move intended to increase international pressure on Downing Street. An official from Spain's foreign ministry said Madrid could use a planned trip to Buenos Aires by foreign minister José Manuel García-Margallo in September to collaborate over Gibraltar and the disputed Falkland Islands off the coast of the South American country. "We are analysing this possibility among several others, such as appealing to the United Nations," the official said. The official declined to comment on whether an approach had already been made to the Argentine government. Boris Johnson, mayor of London, said on Monday that the UK should show the same determination to defend Gibraltar as it showed over the Falklands. "I hope that one way or another we will shortly prise Spanish hands off the throat of our colony," he said, of the 2.6 square mile rocky outcrop on the edge of Spain. Writing in the Daily Telegraph, Mr Johnson said the Foreign Office must recognise that the desire to be British is as strong in Gibraltar as it is in the archipelago in the South Atlantic that Margaret Thatcher went to war with Argentina to defend in 1982. The mayor reminisced about visiting the territory 30 years ago, describing the residents as "almost hysterical . . . in their protestations of Britishness." Royal Navy warships are sailing to Gibraltar this week in a move defence officials stressed was a routine and long-planned deployment. The peninsula has been controlled by the UK since 1713 but Spain has long claimed it. Mariano Rajoy, the Spanish prime minister, has said he would take "all legal measures" to protect its interests in the territory. Spain's possible overtures to Argentina come at a time of historically poor relations between the two countries after the government of Cristina Fernández last year expropriated the YPF division of Repsol, the Spanish oil company. Repsol is suing Argentina for $10bn in compensation and is yet to receive any funds.