This has been bothering me on and off for ages and google has been no help - trying to find the name of a drama serial from my childhood.
I think it would have been the early 1980s - possibly 1982 - and broadcast on BBC1 in the after-school segment.
This is as much as I remember, and it may be incorrect:
It was set in the 19th century. There were children - the oldest one was a girl - and they lived by the sea in a small cottage. Their father was a sailor and he'd been away at sea. He came back to much celebration and sat by a fire drinking, but then fell ill with a fever. He started raving deliriously about a sailor's whistle that had something to do with hidden treasure. He then died. The rest of the series concerned the children trying to seek this whistle.
If this rings any bells with anyone I would be delighted!