Hello, Jazzgirl!
I've watched the relevant part of "Treasures" again!
I had my Readers Digest Road Atlas opened at the Poole area page, too!
Brownsea Island was not mentioned on the programme.
Poole Bay and Sandbanks were, quite a few times.
They had two maps.
One was commissioned by a man called Christopher Hatton, who was one of Queen Elizabeth's "dancing partners"!
They mentioned "gardens" in connection with Hatton.
Wondering if Hatton Gardens in London has a connection?
Henry 8's map had more detail, including "sea monsters", and also showed church towers and beacons which would be lit, in a line, all the way to London, in the event of an invasion.
That is as much as I could glean from the programme.
But, a pity you can not see it, Jazzgirl!
It really is absorbing!