John Silver's Return to Treasure Island: Jim Hawkins is now a young man, newly returned from university. He thinks his days of adventure are all behind him. Whole series seems to be on YouTube, which is nice:

The Box of Delights: technically a kid's show, but one of the best ever, based on a book by John Masefield. Whole thing seems to be on YouTube:

Tales of the Gold Monkey: Always remembered by me as 'Golden Monkey'. Tales of a pilot in an obscure island chain just before WW2. With weird and exotic happenings! Probably all on YouTube, but there's a lot of it, so i didn't check.

There's supposed to be a tweet at the start of this thread explaining that it's a list of old and obscure TV series I like for lockdown viewing. But me being me, of course I forgot! Fortunately, everything seems to be on YouTube.