Nature campaigners have said it is "vital we pick up the mantel" of the movement that secured National Parks for everyone 70 years after pioneers won the right to roam in such landscapes.
Actress Caroline Quentin, president of the Campaign for National Parks, features in a new six-minute film which pays tribute to the people who "lobbied, protested and trespassed" in the wake of the Second World War in the hope of winning access to areas such as the Peak District and later the Yorkshire Dales and North York Moors.
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Their action led to the National Parks and Access to the Countryside Act, which had its royal assent on December 16 1949, and there are now 13 such parks in England and Wales.
The film features the voices of the "visionaries of the environmental movement" as they describe the early days of the campaign.
Speaking in the film, Ms Quentin says: "It's hard to imagine...that just over 70 years ago, the nation of spending time in these places was a radical idea."
The film touches on modern threats to such landscapes, including unsuitable development, climate change and the loss of natural habitats."
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Ms Quentin adds: "Our National Parks are unique and special places that have been enjoyed for generations.
"That’s why it’s vital we pick up the mantle and take on the work that was started 70 years ago. So that future generations can come and enjoy this extraordinary diversity of landscape and the wildlife that lives within it. It’s more important than ever that we continue to campaign for our National Parks.”
The Peak District became a National Park in April 1951, followed by the Lakes a month later.
The North York Moors and Yorkshire Dales were both formed in November the same year.
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The film features Len Clark, who was the last surviving member of the original committee that saw through the 1949 Act. He and his future wife had an unconventional date watching the passage of the bill in the commons that year.
Mr Clark was 102 when interviewed last year, but died last month and "will be much missed by the charity".
It also includes John Foster - who was 98 at the time of the interview - the first person to run a National Park in the UK. He oversaw the early days of the Peak District National Park including setting up the first ranger service in the UK.
Jean Smart, secretary to Gerald and Ethel Haythornthwaite, whose pioneering work led to their beloved Peak District being designated the first National Park in the UK, also features.
In the film, she says: "I just wish more people knew about them - I wish more people in Sheffield knew about them and what they had done, because there's not many of us that do know what they did. And we're all so much better off for it."
Gordon Miller, a former National Park ranger and “legend” of the Peak District, speaks in the film.
Michael Dower, son of John and Pauline Dower - described by the campaign as "visionaries of the movement" - is featured. He reflects on the incredible work of his parents, but went on to be a National Park leader himself.
The film has been featured in Northumberland National Park’s Yours since 1949 exhibit at the Sill: National Landscape Discovery Centre.
Corinne Pluchino, chief executive of Campaign for National Parks said: “This film is in honour of those incredible men and women who dedicated their lives so that we might enjoy some of the most special and spectacular landscapes in the countryside.
“This film is incredibly special to Campaign for National Parks. We were established back in 1936 to lead this fight. It’s been very moving to hear of the dedication of John Dower, the tragedy that inspired Ethel Haythornthwaite to fight to protect the Peak District countryside and to reflect on the incredible foresight of pioneers such as Len Clark who we will sadly miss.”
Tony Gates, chief executive officer of Northumberland National Park said: “We’ve been delighted to feature this film at The Sill as part of our 70th Anniversary Exhibition on the 1949 Act. Our National Parks are the result of great foresight and vision, give so much to the nation and we should never take them for granted; from climate change to mental health, National Parks have as much, if not more, of a role to play in society today than when they were first conceived.
"We hope people who have visited the exhibition at The Sill now feel inspired and motivated to care for the future of our unique National Parks.”