The two navies and air forces are in the South Atlantic for a four-day operation designed to hone their search and rescue capabilities.

The former enemies have taken part in exercises together since the war in 1982 but these have previously been under United Nations auspices. They also involved forces from other countries.

The forces will set up communication links and, in a practice emergency exercise, search for a fishing vessel sinking south of the Falklands.

A Ministry of Defence spokesman said: "The experience has important humanitarian benefits and will ensure that the most effective search and rescue cover is provided for shipping in the area.

"It also represents a positive step in the programme of military co-operation between the UK and Argentina."

Relations improving

Britain's lead ship in the excercise will be HMS Somerset. It will be supported by a Hercules aircraft and a search and rescue Sea King helicopter based in the Falkland Islands.

Admiral Carlos Alberto Marron, Commander-in-Chief of the Argentine Navy, is currently visiting the UK as the guest of Admiral Sir Michael Boyce, First Sea Lord.

Admiral Boyce said: "This is a good example of the way in which defence co-operation between UK and Argentina can produce real benefits not just for our armed forces but for many people who depend on their skills and effectiveness."

Relations between Britain and Argentina have improved steadily since the war.