Think laterally.

I’m sitting in a large tree house in Hoxton Square, east London. It’s not a day out with the kids: this is a quirky new office space, complete with electric sockets, eight desks and available to rent for meetings by local businesses.

It is one of a number of initiatives designed to help fund public parks, the fortunes of which are on a downward trajectory since their genesis in Victorian Britain exactly 175 years ago. The first was created some 130 miles north of where I am today, in the Midlands city of Derby. It was there that in 1840 Joseph Strutt, whose family had made a fortune from textiles, donated an 11-acre plot of land and commissioned a leading horticulturalist, John Loudon, to design a haven amid the smog of the industrial town. The result was the Derby Arboretum – an urban green space that provided a template for the many Victorian public parks that followed in its wake.

 “It was for the mill workers and citizens of the town,” says Prof Paul Elliott, who specialises in the history of parks. “It’s significant because it was free for two days each week.”

Of course, there had been plenty of other green spaces in the country previously, such as village commons, and there were parks and pleasure gardens already in existence, but these invariably charged an entrance fee. The Derby Arboretum, which featured 1,000 different species of trees and shrubs, was specifically created for the public to educate themselves about botany and the glory of God’s creation. It was an immediate hit, with thousands flocking to visit every Sunday and Wednesday.

Before long, similar parks were cropping up around the country, from Victoria Park in Hackney, which was designed to alleviate the terrible health among dock workers, to Birkenhead Park in the Wirral.

It seems odd that these historic green spaces, whose names – Holyrood, Regent’s, Sefton, Wythenshawe – are as much a part of our landscape as the Peak District or the Lake District, would ever charge an entrance fee. But that is precisely what is on the cards once again, because park budgets are being cut. They are not a statutory service and local authorities, which fund the great majority, are under little obligation to maintain the planting of trees and shrubs or the upkeep of paths.

And so it is that some parks are starting to cast around for alternative sources of funding. The Hoxton tree office is one such source, but it is not without its problems: the £40,000 structure is leaking slightly and is clearly not designed for soggy autumn weather. It is also sited just four feet off the ground, making it impossible for park users to play football or picnic beneath. After a year in situ, it has only reached 25 per cent capacity.

If a library closes it is immediately obvious. But if you gradually cut back a park’s funding, it’s harder to notice. Grass is mown less frequently, trees start to decline and die

But Lydia Ragoonanan, programme manager for the charity Nesta’s Rethinking Parks project, says innovations that don’t work are just as important to trial as those that do.

Formerly the National Endowment for Science, Technology and the Arts, Nesta helps fund various innovation projects, giving small amounts of money to test out new ideas. Over the last year or so it has been funding 11 different schemes for parks to cut their budgets and raise more money.

“We’re here to help stimulate new ideas and test new ideas, to find new money or cut costs to maintain public parks,” Ragoonanan tells me in the treehouse.

Some ideas are fairly basic. In Sheffield’s Heeley Park they are trying to develop a subscription model by offering members preferential treatment for concerts held in the park. Others, like the Hoxton treehouse, are quirkier.

The aim is to find more crowd-pleasing solutions than some that have already been put into practice elsewhere. There was uproar among residents last year when Battersea Park in south London turned over part of its much-loved – if slightly dilapidated – adventure playground to a private company, Go Ape. Locals will now have to pay an estimated £25 a session when it opens later this year, whereas previously it was free.

In Liverpool, more drastic action is afoot. The city’s mayor has announced plans to sell Sefton Park Meadows, an 11-acre green space, to a house-builder. Kim Cattrall, the Liverpool-born actress, has expressed her horror, and duly been attacked by the mayor, who claims she is out of touch and he has to cut the £10 million annual parks budget by half.

There are no figures for how much it costs to maintain the estimated 27,000 public parks in Britain, which cover more than a third of a million acres, an area nearly the size of Greater London. But a survey by the Heritage Lottery Fund last year found 86 per cent of park managers had seen their revenue cut in the previous three years.

We are having to make huge savings. We will have lost 50 per cent of our staff – down from about 90 to 45. But the area of parks remains the same and the public expectation as to the quality of the parks remains the same.

At the Derby Arboretum the dwindling of funds is starting to show. Many of the gates are locked up, the public lavatories are out of order and there is some litter under the trees, including those ubiquitous little metal canisters that contain the legal high nitrous oxide. Four years ago there were 33 full-time rangers. Now there are just 13.

Walking around the place, I meet Michael McNaught, the community park manager. Would he consider charging an entrance fee?

“I must confess my thinking is how you keep it free for the locals of Derby but maybe charge for people coming to visit,” he says.

Ninety miles north, Burnley’s 400-acre Towneley Park has converted well over 100 acres to wild flower meadows. This move away from mown lawns is not just because natural planting has become fashionable. It is also much cheaper. Simon Goff, the head of green spaces in Burnley, says each acre they no longer have to mow using tractors saves around over £1,000 a year.

Other ideas they are testing out include asking farmers to mow the grassed areas and keeping the hay as payment; selling timber grown from the park’s woodland; replacing biennial bedding plants with perennial flowers; using felled trees to fuel woodchip boilers that heat the park buildings; and growing the herb borage, used to make starflower oil, on a commercial basis.

“We are having to make huge savings,” says Goff. “We will have lost 50 per cent of our staff – down from about 90 to 45. But the area of parks remains the same and the public expectation as to the quality of the parks remains the same. So do we just spread the butter very thinly or do we try and find a different way of managing some areas?”

It is simply not possible for all areas of the park to be just as well maintained as before, he warns, yet the public should be able to enjoy just as good access to nature after the changes.

But as Prof Elliott says, parks need long-term funding. “If a library closes it is immediately obvious. But if you gradually cut back a park’s funding, it’s harder to notice. Grass is mown less frequently, trees start to decline and die. It’s incremental.”

To allow public parks to decline would see a diminishment of public life, he argues. “They are part of the character of Britain.”