The problem became so severe that British aircraft were ordered to try to avoid travelling over the sea because too many being drowned, it has emerged.

Amid the 70th anniversary commemorations this summer it can be disclosed that at least 200 pilots died “needlessly” in 1940 after bailing out over water.

Once they hit the water there was very little chance of survival with only the occasional flier being picked up by a passing destroyer or fishing boat.

The German service, that had been set up in 1935, became so effective that RAF chiefs ordered fighters to shoot down the Luftwaffe Dornier 24 seaplane that were unarmed and painted in white with a large red cross. However, it is thought that the Germans might have been using the aircraft for illicit reconnaissance missions.

“This was one of the most shameful and disgraceful episodes of the entire war,” said Dr North, author of ‘The Many’ to be published next year.

“For an RAF airman to be shot down over the sea was an almost certain death sentence if the German rescue services were not close at hand.

“Many a good fighter pilot was lost who would have been invaluable in the days that followed.”

An estimated 80 per cent of downed pilots died over the sea whereas the rate dropped to 50 per cent over land. On Aug 8 it is believed 15 out of 18 airmen who bailed out were lost at sea.

Frustrated at the poor rescue effort a New Zealand pilot, Flt Lt RF Aitken, “scrounged” a Walrus flying boat from the Fleet Air Arm and saved 35 British and German airmen over the summer.

Air chiefs had assumed that the high volume of shipping in British coastal waters meant that downed airmen would be spotted and recovered.

But by August 19, Air Vice Marshal Sir Keith Park, who commanded the fighter group in the south east, ordered his flight controllers not to vector pilots over the sea because “too many were getting drowned”.

The critical shortage of pilots came very close to costing the British the campaign and it was only when the dogfights were fought over land did the tide begin to turn.

It was not until 22 August when an emergency meeting was held under the chairmanship of Air Marshal Sir Arthur “Bomber” Harris to explore the shortcomings of air sea rescue provision. Only in late 1941 did the Air Sea Rescue Directorate become functional and by the end of the war the RAF went from 18 rescue launches to 600 plus squadrons of dedicated aircraft.

On the day that celebrated Winston Churchill’s speech on “the few” on Saturday the RAF were once again without a full-time search and rescue service with its Nimrod reconnaissance aircraft mothballed to save cash.