The Weekend's TV: Ocean Giants, Sun, BBC1<br/>Britain's Hidden Heritage, Sun, BBC1

I seem to be making a habit of writing about Leviathan.

Last week, I said that an Inside Nature's Giants Special on the sperm whale was one of the best nature documentaries of recent years. Last night, the very different Ocean Giants was also superb. As new hobbies go, whale watching is a treat.

Whereas last week we concentrated on a beached sperm whale on the Kent coast, last night's show had the very different task of finding and following the biggest animals on Earth in their element – the ocean depths. As so often with modern documentaries about the natural world, the focus was split between the beasts of the big blue, and those devoted cameramen who bought us pictures of them in daring raids on their territory.

We met many different whales, the best of which was the extraordinary and mysterious bowhead. These creatures are not the biggest of their order, but in living up to 200 they are the oldest of all mammals. Their longevity is directly related to their size. Bowheads have 50 tonnes of insulating blubber, which enables them to have a lower body temperature than any other whale. The lower your temperature, the longer you live. And because (uniquely among mammals) the bowhead's backbone never fuses, they carry on growing until the moment they die.

Even then, they cannot match the size of blue whales, the biggest species that has ever lived, which the show closed with. I know it's a terribly mundane point, but the thing about size is that it is relative. If you go into the Natural History Museum, you can see the size of a giant whale in real life. On a screen, that is impossible, because the whale's length is compressed to something around 30 inches. It is therefore necessary to provide some sort of relative measure – a human swimming alongside, or a double-decker bus, for instance. I watched this excellent show with my brother, and we both felt there was a failure to convey the sheer size of these beasts because the only thing we had to compare them with was each other.

Against that, some of the underwater photography was stunning, and bravely acquired because a set of marauding males were fighting for the affections of a female. There was the customary (and necessary) update on blue whale numbers – 300,000 two decades ago and 10,000 now, though climbing – and anger about the impact of climate change on their habitat.

This came from the scientists on expedition rather than Stephen Fry, who shares their concern about a hotter planet, and was reliably magnificent as our narrator. What animated Fry was a sense that through perseverance and passion, these mysterious creatures could become familiar.

The conceit of Britain's Hidden Heritage was rather similar, but it didn't work because the heritage isn't hidden. "Hidden" was used for its alliterative quality, not its actual meaning.

Far from being mysterious or concealed from view, many of the great institutions we toured are right before us, if only you make the effort to look. That was the real clarion call of the BBC's latest version of Sunday night patriotism, a kind of bigger version of Antiques Roadshow. Charlie Luxton, Clare Balding, John Sergeant and presenter Paul Martin toured various relics of bygone ages, each making the point that Britain's history is richer and more diverse than many of us imagine.

The focus of the action was Dumfries House in Ayrshire. We started here, left, and returned to it. Martin took us on a tour of the 18th-century Palladian mansion, making the point that it was rare among such places in having retained much of its original furniture. Two cleaners, who would spend several weeks polishing the same brass mantelpiece, conveyed the devotion such history can inspire. And in doing so, they were a prelude to a fawning interview with the benefactor of the house, HRH the Prince of Wales.

Our future king explained that he was inspired to get together some investors, and save the house from private ownership, by the prospect of it being thereby ruined. It is now open to the public, though in need of corporate and wedding bookings if it is to be saved. Doubtless this publicity will help, and a jolly thing too. But Martin and his script-writers should have delved further into its history – as Luxton, Balding and Sergeant did on their respective projects. Instead, here we had only cursory glances at beautiful rooms, rather than rich narrative. This promoted ornamentalism above history, which naturally made the story less compelling.

a.rajan@independent.co.uk / twitter.com/amolrajan