London’s local authorities have issued a stark warning: if government cuts continue on the same trajectory, the capital’s boroughs will not be able to prevent a “slide towards privately-run parks” by the end of the decade.

But how big is the risk? Who owns the nation’s parks? Are they underfunded and are they being sold off to private buyers? Here we answer some of the key questions.

How many public parks are there in the UK?

There are approximately 27,000 public parks. But that figure comes from a 2001 survey, so it’s hard to be sure of the exact number. The Heritage Lottery Fund (HLF) carried out research into parks in 2014 but its head of landscape and natural heritage Drew Bennellick says: “There were quite a few local authorities who couldn’t tell us how many parks they’ve got or how much land they’ve got.”

An added problem, says Bennellick, is that planning guidelines that set out the definition of a park have been abolished, so there is no longer an agreed typology.

Fortunately, Natural England and Ordnance Survey are working together to produce a free comprehensive map of all open access green space in England. Scotland already has its parks mapped out.

Who owns the public parks?

Most public parks are owned by local authorities, although London’s royal parks – such as Hyde Park and Richmond Park – are owned by the Crown and run by a government agency called the Royal Parks. Many local authorities were given their parks by benefactors for the benefit of local people.

How are public parks funded?

Local authorities pay for the running of the parks. Their budgets have been slashed in recent years, however, and many councils are choosing to focus spending on their statutory obligations, such as social care. The 2014 HLF report found that 86% of park managers had seen their revenue cut in the previous three years.

Parks have, however, been winners in the UK’s national lottery. Over the past few years, they’ve received £620m from HLF and £80m from the Big Lottery Fund (BLF), which has helped to revitalise many run-down public spaces. There are 5,000 Friends groups in the UK – community groups that support their local parks through volunteering and fundraising. They generate about £30m a year for parks, according to the HLF report.

On Monday 29 June, the HLF and BLF will jointly announce another £34m to enable councils to introduce or refurbish public facilities in parks, such as cafes and toilets.

How many parks are being sold off to the private sector?

Nobody knows – there is no central body gathering this information. It’s unlikely, says Bennellick, that we will see the wholesale sell-off of big public parks, because of the outcry this would generate. “You’d have to be a brave politician to suggest selling off an entire park,” he says.

But there are other risks. The HLF report found that just under half of all councils are planning to dispose of some of their green spaces with 19% considering the disposal of parks. Some councils, however, are selling off bits of parks for development.

Liverpool’s mayor is planning to sell off Sefton Park Meadows, 11 acres of land that adjoin Sefton Park, to developers. It also plans to develop Walton Hall Park into Everton FC’s new ground and in another park, Woolton Woods, it is planning to rebuild a local school.

Local people have organised to fight these proposals. Stephen McNally, chair of Save Our Green Spaces Liverpool, says of the Sefton Park Meadows proposal: “It’s only a small piece of grassland on the edge of the park, but it’s aesthetic to the area. Yet the mayor has indicated a company can come in and build 30 houses on it. There’s no need for them – it changes the whole dynamic of the area. The local people are up against it.”

Some councils, says Bennellick, are also selling off small pieces of natural land and sports facilities, such as football pitches. County councils, for example, are handing over management of parks to other organisations such as wildlife parks: “My concern is that the wildlife trusts are keen to take some of the better sites, while some of the sites that may be more marginal but just as valued end up getting stuck with the county council who have got rid of their ecologists and countryside rangers, and those sites will get worse.”

Is there any other way of funding parks?

Bennellick points out that many councils hire out parks for fairs or sporting events, and these bring in much-needed cash. Nesta is currently working on a project, supported by the BLF, to explore new models of financing and managing public parks, which could include raising money by allowing businesses to use parks for particular purposes, such as product launches.

A spokesperson for London Councils, which represents the capital’s 32 boroughs, says: “An alternative model of maintaining parks and green spaces without privatisation would be transferring them to volunteers, community interest companies or trusts. The National Trust recently announced it would look at how it could work with councils to protect green spaces.”

What next?

Bennellick would like to see a national organisation, similar to the US Center for City Park Excellence, which stands up for the interests of parks, gathers data and shares good practice.

“There’s a complete lack of collaboration or sharing of knowledge across the sector,” he says. “There’s lots of really good things going on around the place, but no key organisation that stands up for UK parks that can be identified as a champion for public green space. And that’s a real problem – there’s some really good innovation going on but it’s not shared, and a lot of people are reinventing the wheel.”

• We want to know how many local parks are being affected by the prospect of privatisation. If your parks are under threat, share your story with us via @guardianpublic or email us: public.leaders@theguardian.com

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