Can anyone identify this 1980s children's TV serial (v. limited info, sorry)

[PlaitBilledDuckyPuss]

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!

And PS I'm another one who was never allowed to watch ITV as a child. My dad had ideas above his station I think!

I was reminded to search for it (again) because I've just been watching The Box of Delights (charity shop DVD find that I saved for Christmas) which is powerfully nostalgic - it was on in the Sunday afternoon slot in the run up to Christmas 1984.

I can see where I went wrong with The Little Silver Trumpet as I'd forgotten the 'trumpet' bit and was searching for things with 'whistle' in the title.

The theme tune is part of Faure's Pelleas et Melisande - I knew there was a children's drama I'd watched that had that as a theme tune, but I'd misremembered this as being 'A Little Princess' and didn't connect it with the 'whistle' series.

I see the series was based on a book, so I might get that ordered too!