Wrecked German aircraft (Me 109E, He 111 and Ju 88A) in Britain, 1940
Source Dennis Richards: Royal Air Force 1939–1945. Volume I: The Fight at Odds; London, HMSO, 1953. (Official history of the RAF photo in the public domain)
One of the odds working in the favor of the Royal Air Force in the Battle Britain was the air battles were often fought over Britain. If their planes had been damaged too badly to stay in the air, RAF pilots bailed out over England and lived to fight another day.
Under British military escort, two captured Luftwaffe crewmen walk out of the London Underground, 1940 (Imperial War Museum)
German pilots who bailed out became POWs or in the acronym used at the time, “PWs.” The pilots above would be taken to one of the interrogation facilities in London and later sent to a POW in Britain, or Canada or other places in the Empire. Germans and Allies followed the Geneva Convention protocol by notifying international Red Cross of name, rank, and identification number of men either taken prisoner.
However, if you were an RAF pilot (or German pilot) shot down over the English Channel and no one saw you go down or no ship came by, hypothermia killed within four hours give or take. The temperature of the water was about 57 degrees during the summer. (The Most Dangerous Enemy: A History of the Battle of Britain)
Efforts were made by both sides to rescue pilots shot down in the English Channel but one man afloat in a small raft or just a Mae West lifejacket such as RAF pilots wore, was hard to spot. Both sides used high speed rescue launches operated by their respective air forces, float planes as well as naval vessels to rescue their men. While they would not search for the pilots of the other side, if they came across one, Air/Sea rescue of either side would rescue them.
However, a centralized and trained air/sea rescue force was not organized by the RAF until 1941. They did have float planes and some high speed rescue launches (operated by the RAF) in the Battle of Britain but without the command and control which was so much a part of the ethos of Fighter Command. It is a surprising oversight.
Obviously, the RAF had a steep learning curve to master to operate their rescue launches with any efficiency. In August of 1940, in a move of more desperation than anything else, the RAF passed control of their handful of rescue launches to local Royal Naval Commands on the Channel. Unfortunately, during the Battle of Britain pilots who ditched in the English Channel died in large numbers.
Prime Minister Churchill gave orders that German rescue float planes marked with a red cross were to be shot down over the channel or destroyed if they had landed in the water. I have not been able to determine if this were done or how often it was done.