'Two hundred miles off the coast of New Orleans, in the clear blue open sea, I'm starting to know what being in deep water means. My dive computer is going nuts, beeping an alarm in rapid descent. 43, 44, 45 metres, soon I'll be deeper than a scuba diver on air can safely dive. I'm tumbling head over heels like an ostracod - one of the many strange creatures here that defy our imagination. It's hard to say what's up or down. I'm in freefall, an aquanaut lost in space.'

The Whale in Your Room follows the thrilling adventures of BBC Blue Planet producer, John Ruthven, on a journey of discovery that helped the marine world flow into your living room via the TV.

For many, the oceans are missing pieces in the story of life on Earth, and it doesn't help that most are blue and form by far the biggest part of the jigsaw. Quite literally immersed in his subject, John can put them together, as the only producer to have worked full time on Blue Planet series I and II, and nearly fifty other films about the sea. With first-hand experience he feels the loneliness of whale calves in the blue, the fear as seals dodge great white sharks near the coast, or the curiosity of octopus staring back at the camera. His journey take us through the blue rings of South Pacific coral atolls, gives us submarine rides into the abyss with ancient life forms, and encounters so close with singing humpback whales that the water will bounce at the bottom of your virtual dive mask. Through each stunning adventure John draws out important insights into what is presently known about how the sea, and our whole blue planet works.

'As a boy in the sixties I was part of the Apollo nerd generation and like many of my peers I wanted to be either an astronaut or a diver and filmmaker like Jacques Cousteau. Curiously neither of these options was ever suggested as a realistic possibility by careers advice at school. So it was with great surprise that I found myself, twenty years later, in charge of a film crew off Mexico, trying to get the best ever shots of blue whales. Just shows - never stop dreaming!'

Like the Blue Planet series itself, the stories of the ocean are broadly divided into the major habitats of the ocean, of the deep abyss, the coasts, the open seas, the coral worlds, green underwater forests and the polar regions. As John points out:

'The Aboriginal Australians call the sea 'the saltwater country', which I think is a beautiful understanding of the ocean, in that it's not a plain blue at all but when you look closely it's all the colours of the rainbow. When you get to know it, each part is distinct and can be mapped, just like the land. And at night there are even bright patches of animal light, so in many ways we live not on the blue planet, but the glowing planet.'

What creatures could remain undiscovered in the 95 per cent of the seas that have not been thoroughly explored? The surface of Mars and Venus are better known to us than the seabed. Yet to map the world's ocean to even 100-metre blocks of accuracy, something that environmentalists say is essential for its protection, could take a further 300 years. Even creatures that are known, such as the giant squid, have proved too hard to film to date. John has also been involved in the attempts to film this massive creature, using high-tech cameras deep in the abyss, with only the light of the moon for illumination. The thread of his story is to take us through such challenges of underwater imaging, as we develop ever better technology, to where no human has gone before, and see further than ever into the deep.

The Whale in Your Room, like the proverbial 'elephant in the room', is also about how, until recently, we have been largely blind to our pollution of the seas. So, for example, John explores how plastic 'went wild' in the ocean, tries to understand how we got into this mess, and see if we can ever untangle the oceans from its grip.

'1,500 miles from nowhere I find myself landing on what seems an idyllic tropical island that has been uninhabited for 40 years. I wade ashore through a tangle of nylon fishing gear, plastic bottles up to my knees, flip flops, Crocs, syringes, food packaging, plastic bags and disposable razors. I wonder if any of the brilliant chemists who invented this material ever considered this after-use nightmare.'

In Blue Planet II the story John produced about a dead whale calf carried by its mother, likely killed by plastic residues, touched a nation. It ignited an already simmering public opinion into doing something about the plastic choking our seas. John was surprised to hear it being discussed in the UK parliament the day after broadcast. Such a depth of response, a connection and empathy with the sea, showed promise for real change. What creates moments like this? What makes people sit up and take notice at a certain point in history, when all along NGOs and scientists have been telling us the same thing, and the signs have been obvious? Is there hope for the ocean's future?

On our journey, memorable, touching and often funny moments with film crews at sea will help to explain our current understanding of the ocean and how little we still know about our home planet.

At the moment John is filming sperm whales in the abyss for the Discovery Channel, devising techniques for the whales to film themselves and switch on their own cameras with their hunting clicks as they go through schools of giant squid. Also for National Geographic he's helping to plan new structures for living underwater, and as a possible base for a new immersive film series.