Whenever David Attenborough speaks, the world listens – so his latest BBC programme, which heralds the broadcaster’s 100th birthday, is bound to attract attention.

Secret Garden, which features five different UK gardens, might not be what people normally expect from Attenborough, says the show’s series producer, Bill Markham, as “there’s no lions and tigers”.

But he hopes it is “much more relatable” as it focuses on where Attenborough’s interest in natural history began: on home turf, with the veteran presenter stressing the importance of what is happening “right on our doorsteps”. He reveals that “some British gardens are almost as diverse as a tropical rainforest” and that “our gardens cover a greater area than all of our national nature reserves combined”.

The programme aims to ease eco-anxiety, featuring changes viewers can make to help wildlife, including some which people might find contentious.

Secret Garden estimates that the 9.5m pet cats in Britain may kill approximately 55m birds every year. Attenborough reveals that putting bells on cats “reduces pet cats’ hunting success by a third”, and raising bird feeders higher also cuts deaths.

Markham explains the current situation is “unfair on the prey”, because cats are “the biggest predator in our gardens [but] they’re being fed every day. There’s no limit on their population. So the normal relationship between predators and prey falls apart.

“What would work really well is if people kept their cats indoors during bird breeding season,” he says, citing an ecologist called Dr Davide Dominoni whose studies show that keeping felines indoors during April and May “would reduce their impact massively”.

“We didn’t want this to be a preachy series at all,” says Markham. “Not everyone likes to do this because they think their cat has a right to be out. There are a lot of cat lovers who feel very strongly about this. But if you also love your wildlife, and I think we’re a nation of animal lovers and we’re a nation of gardeners – then I think you can do your bit.”

Another episode covers pheasants, which “originate from Asia, but every year more than 30m are released into the British countryside” where they eat native insects, reptiles and amphibians.

The countryside lobby argue that shooting provides rural jobs. But Markham points out that, despite the trend for reintroducing native species such as beavers, “Every year, we unleash this scourge on the countryside. It’s messing with the ecology.”

Such calls to action could replicate the success Attenborough’s voice had in reducing plastic pollution following Blue Planet II. He is unafraid to take on the big issues as he approaches his century: last year in the film Ocean, released on his 99th birthday, Attenborough made an urgent, passionate case against the ruin caused by industrial overfishing.

Cat owners and the countryside lobby might argue that Secret Garden is one of the most contentious UK-focused natural history shows narrated by the presenter. But Markham says the UK loves “animals, gardens and David Attenborough”, so if Secret Garden “succeeds in encouraging people to rethink what their gardens can be, it will be in no small part due to his influence,” he says.

Despite his years of experience, Attenborough was “surprised by the incredible things living in our gardens”, Markham adds. “Probably the first animal he ever saw was in his garden, and that, quite conceivably, set him on the path of being the world’s greatest naturalist.”

Markham also hopes the show will be comforting, as “a lot of us have eco-anxiety. We’re worried about climate change, and feel there’s nothing you can do as an individual.

“But what you can do is go out into a garden. There are 25m gardens in the UK – 80% of us have got access to gardens and you can make one or two little changes.” He gives the example of planting a cheap native tree, which helps increase the supply of caterpillars for birds.

The idea for Secret Garden grew out of our increased interest in gardening during lockdown. Markham calls gardens “unsung heroes”, where the “laws of the jungle still apply”, and an average patch can contain about “2,600 species of animal and plant”.

Highlights of the show include a pine marten hunting sand martins in the UK, filmed for the first time; an otter hunting ducks; mayflies and damselflies fighting in a scene similar to the famous “snakes v iguana” sequence from Planet Earth II; and field mice leaving landmarks to find their way home, Hansel and Gretel-style.