Conditions - Excellent visibility, light to moderate N/NW winds, Sea State Slight/Moderate, temperature 18/20C, sunny.The party leader has apparently done the route a number of times before and both had previously climbed in Scotland in winter and the Alps. I am a qualified and experienced Mountaineering Instructor, very familiar with the route. At approximately 1200hrs I was descending the approach abseil of Commando Ridge to join my client on the slabs at the base of the route. On looking over my shoulder i saw a helmet in the water in the cauldron between the broad slab and the base of the ridge proper. I realised there was a person apparently swimming in the impact zone next to the base of the cliff. i quickly descended and ensured my client (herself and experienced climber and former rescue team member) was safe before heading down the slabs to establish what was happening. On getting to his partner, who was sat above the waters edge, it quickly became apparent that the swimmer had slipped into the water on wet polished rock. He had by that time reportedly been there for approximately 6 minutes and was now struggling to stay afloat while being washed against the rocks. His partner had set up a makeshift daisy-chain of slings / carabiners anchored to a bollard which he was trying to get the swimmer to clip onto. (worth mentioning at this stage that the swimmer had been carrying the rope; which he lost on entry). The swimmer then managed to get onto a small wave washed platform just a few feet away which offered an opportunity for me to get in and clip the daisy chain to him. He was then hauled onto a ledge just clear of the water where he collapsed with exhaustion, remaining verbally responsive. the decision was taken to move him up the slabs away from the rising tide, which was done with the assistance of his partner and my client using a hoist. The casualty had clearly swallowed a lot of water, was pale and exhausted but otherwise uninjured and stable. the casualty was made safe and comfortable on the slab before calling the emergency services from further up the ridge. The call to the emergency services was made at around 1228hrs. At approximately 1300hrs a coastguard helicopter, two lifeboats and coastguard land team arrived on scene. The casualty was quickly airlifted to hospital for further treatment.