Thanks Geoff, - My house is 450 yards from the sea (at the moment- the cliff is eroding alarmingly but should see me out) and we get some interesting fossils on the beach that came out of the gllacial till, so perhaps it got deposited in what is now my potato patch during the ice age! If it was relatively fresh I might think a bird had dropped it.
We collect coal on the beach , hand pick it, mainly small bits but sometimes larger chunks if we are lucky- it's free, burns hot and a shovelful lasts a couple of hours. Every so often we use it when the logs are wet or too green.