He may be turning 94 on 8 May, but our beloved naturalist and broadcaster Sir David Attenborough shows no sign of slowing down.

Today, ‘the nation’s grandfather’, as some have called him, gives the impression of being a man on a mission. As charismatic in the flesh as he is on screen, he wants to continue to raise awareness of the disastrous impact humans are having on nature and to let us know what we can do about it.

‘Politicians need convincing this is a very serious problem,’ he urges. ‘We hope they are going to take responsible decisions – if necessary, ones that will cost us.’

His new film, David Attenborough: A Life on Our Planet, is his witness statement for the natural world – and there is surely no one we trust more to tell us the truth.

In a career spanning seven decades, he has visited every continent on Earth, producing multiple ground-breaking television series and programmes for the BBC that have become ‘part of the national psyche’ – as Prince William put it in 2016.

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In his new film – which was produced by award-winning wildlife film-makers Silverback Films and the WWF, and will play on Netflix later in the year – Sir David reflects on the seismic changes to the natural world he’s seen during his life.

‘When I was a child, nature was the great unknown – out there. Municipal councils on the coast of Great Britain were tipping raw sewage into the sea when I was a boy on the grounds that the sea was infinitely large and would wash it away.

‘The sea was infinitely big. The rainforests extended forever. Animals proliferated all over. The fact that by this stage we’d already exterminated whole species was conveniently forgotten.’

Sir David with the Duke and Duchess of Cambridge | Getty

This is not the first time Sir David has alerted us to what is going on. He investigated the global environmental crisis for the BBC in State of the Planet in 2000.

‘I said then that it’s going to take major social and political change. Nobody took a blind bit of notice.’

Now, the situation is more urgent than ever. ‘We all have a carbon footprint, we’re sitting here breathing out carbon dioxide like there’s no tomorrow,’ he says. ‘But that doesn’t mean you have to wear a hair shirt. Producing carbon dioxide is inevitable. We can’t suddenly say we’re going to stop living. All you can do is ensure, as far as you can, that you live by certain standards.

‘Yesterday, I thought, “I’ll put on a jersey instead of turning on the electric fire.” Of course, you do those things. But let’s not say, “Forgive me for breathing.”’

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As ever, Sir David’s is a dependably calm voice. But there are still some things that make him angry. ‘I get letters that drive me absolutely spare. I got sent a letter about how important it was to care for the planet, which was sent in a completely pointless plastic envelope. Ludicrous!’

For his own part, Sir David tries to take more care. ‘I live in a reasonably modest fashion. I don’t believe in excess, in luxury.

‘I must be careful though,’ he adds quickly, ‘Or I’ll come out sounding like Saint Francis!’

He’s the first to admit he hasn’t always been quite so saintly – at least by today’s standards. Indeed, back in 1954, his first series for the BBC, Zoo Quest, saw him travelling the globe with a team from London Zoo, in search of exotic animals.

‘When I started, my major films were about jumping on animals and putting them in sacks and dragging them back home to Regent’s Park. That’s how it was. That’s how we saw the world.’

He finishes with a smile, ‘We know better now.’