But these aren't rock-hard fossils. They were baked into the silt and covered with sand and later deposits which have protected them ever since. Now erosion is uncovering these ancient silts, but what the sea reveals it also destroys - the footprints last only until the next high tide or a few weeks at most once exposed.

Gordon calls it "ephemeral archaeology". Or "extreme archaeology" because he goes out in all weathers, accompanied as always by his dog Kim, to record these fleeting remnants of prehistoric life before they disappear for ever. It's something that only an amateur archaeologist, retired and living nearby, could have the time to do.

In this programme Gordon takes us through the process of discovery, helped by his wife and plaster-caster Pat (also a retired teacher), retired archaeological chiropodist Phyllis Jackson, and academic specialists in prehistory. Their records of children's feet are particularly important - because little is known about the place of children in prehistoric society.

A group of present-day school-children join Gordon on the beach to compare their own footprints - walking, running, playing - with those of their 5,000 year old ancestors. A clue perhaps to a riddle that still puzzles him - what were those prehistoric children doing on the beach? Helping their parents? Or just playing?