Jan,
Unlike the Belgian coast, there are lots of shingle beaches around the south coast of England. Extremely uncomfortable and exhausting to walk on and if the tide is low and sand is visible, that is the place to walk.
Unfortunately, that meant the Morane pilot had to choose between ditching and the shingle. I am amazed that he successfully landed without nosing over. A very good job that he attempted a three-point, tail-low landing.