Royal Navy warships are to set sail for the Mediterranean amid continued diplomatic tensions with the Spanish over Gibraltar.
The type 23 frigate HMS Westminster will dock in Gibraltar as part of the exercise, while other ships in the task group expected to visit Spanish ports.
The vessels, which include helicopter carrier HMS Illustrious, will be taking part in what defence officials stressed was a long-scheduled deployment codenamed Cougar '13 in the Mediterranean and the Gulf.
Four Royal Navy warships, the lead commando group from 3 Commando Brigade Royal Marines and elements of naval air squadrons will be supported by five vessels from the Royal Fleet Auxiliary.
Commodore Paddy McAlpine, commander UK Task Group, said: "Cougar '13 is a bespoke opportunity to enhance the Royal Navy's enduring core skill - the ability to operate and project power as a task group at range. In so doing, it will also remind interested domestic and international parties of the enduring utility, employability and interoperability of the Royal Navy. During Cougar '13 we will engage with our partner nations through a series of exercises, reinforcing our commitment and demonstrating our contribution to security in the Mediterranean and Gulf region."
The vessels set sail from Portsmouth as a diplomatic spat continued between the UK and Spain, triggered by the creation of an artificial reef by the Gibraltarian authorities which the Spanish claim will destroy fishing in the area. Madrid responded by beefing up border controls, leading to lengthy queues, and suggesting that a 50 euro (£43.30) fee could be imposed on every vehicle entering or leaving the British overseas territory through the fenced border with Spain.
On Sunday, the Royal Gibraltar Police tweeted that Guardia Civil checks had caused queues of up to two hours at the border, with Spanish officers checking "every car" going into the Rock.
Spanish defence minister, Pedro Morenes, has meanwhile said that it is "totally normal" for British warships to dock in Gibraltar in what is a "routine visit", according to reports. Mr Morenes reportedly told the Europa Press news agency: "Neither the British nor the Spanish government have an interest in there being bad relations."
He also said that aircraft carrier HMS Illustrious had requested and been granted permission to stop off at the southern Spanish naval base of Rota on August 18, proving that there was no military escalation between the two countries.
Writing in The Sun, Europe Minister David Lidington said: "Britain and Spain matter to each other. We are Nato allies, key trading partners and millions of Brits travel to Spain every year. But our good friendship with Spain does not mean we will turn a blind eye when the people of Gibraltar are threatened or put under pressure. Gibraltarians are as British as you or me and rightly proud of it."