In summertime games on public parks are the delight of everyone.

Softball is one such game, and it is easy to play. There is no need for any pitch markings. With some basic equipment, anyone can pitch up to a public park and enjoy a game of softball.

This is what happens every summer at Hyde Park, managed by a body called the “Royal Parks” – described as “an executive agency of the Department for Culture, Media and Sport”. One part of Hyde Park is especially suitable for people who just want to pitch up and play any game, away from joggers, dog-walkers and picnickers who may be hit by stray balls or otherwise interrupted. It is called the “Old Football Pitches” and is just by the Albert Memorial.

And ten years ago, some charity workers came together to play softball on the Old Football Pitches. Quite soon it became popular and a league was formed, the London Charity Softball League. This was organised by the charity workers themselves.

Out of this some very good things happened. This was not part of a grand plan, and it was not the result of any “communications strategy”. Ideas were swapped and thoughts exchanged. Charities gained insights and information about good practices from other charities without spending their donations on consultancy advice, and suitable people were hired without donations going to employment agencies. Significant savings were thereby achieved. It became an efficient and cost-free example of spontaneous civic association to which no sensible person on the left or the right could object. Anyone supporting or benefitting from the charities involved benefitted from this, and it has not cost those involved a penny. And all this was possible only because of the free access to a public space. It was, in its way, a quiet testament to what people freely coming together can do for the public good.

But the league is now likely to come to a sudden end. Tonight’s two matches – the end-of-league trophy and plate finals – will probably be the last played in this annual competition. A wonderful and cost-free public good may now be extinguished, and other similar public goods will be prevented from spontaneously emerging.

This is because of a sudden Royal Parks “change of policy”. Instead of the charity workers having free access to the Old Football Pitches, they will have to pay a total of an estimated £6,000 each summer, and if the charges are not paid then the police will be called. These charges are supposedly for the “management” of the space, but nothing has actually been done to improve the Old Football Pitches. The only change is that there are now charges when there were no charges before. The change of policy was not announced on the Royal Parks website and nor was there was a press release. There was even no consultation with the groups which had used the Old Football Pitches for years for free.

The enforcement of these charges have been given to a private company, who happened to manage the adjacent tennis courts. There was no procurement exercise for this new management role for the company; a simple expedient of varying an existing contract was adopted. The Royal Parks have refused to disclose this contract because of “commercial sensitivities” – which is odd because the Royal Parks also say this is not a commercial issue at all and is only to do with the management of a public park. The company is to keep a percentage of what they collect and will give the rest to the Royal Parks. This percentage, or the envisaged amounts involved, will also not be disclosed by the Royal Parks as it is “commercially sensitive”. But the fact is that the Royal Parks want it both ways: they want to say it is a commercial matter when it comes to not disclosing information, but to maintain it is not a commercial matter at all when they want us to nod along with their assurances that no one is making money out if it.

This is part of a trend. Hyde Park, like many other public spaces, is now shifting into becoming a “venue” and usage is becoming a revenue stream. What are public goods are being turned slowly into private goods: you will get what you pay for. The deputy chief executive of the Royal Parks even assured the charity softball players at a recent meeting that one often only appreciates something if it is paid for. (When I asked for clarification on this, I was told the press officer's "recollection was that the Deputy CEO was pointing to a specific body of research that indicates sports bookings are more likely to be kept when a small fee is taken in return for the space".)

There may be a case for charges to be made for usage of the Old Football Pitches; but the stark reality is that had those charges been in place eight years ago, the London Charity Softball League would not have come into existence, and all the cost-free benefits which have since flowed from this would never have happened. That is how public goods work: the benefits cannot be foreseen or quantified with certainty and fitted into neat business plans.

In the circumstances, the imposition of charges for usage of the Old Football Pitches has been a practical mess. The company has produced inconstant maps for the players as to what parts are still free to play on. An “administration fee” was announced out of nowhere, and then reduced. The rates to be charged were similarly declared, and then “discounted”. It all smacked of being made-up as it went along. And as the summer went on, fewer people played on the pitches. If the intention was to have the “efficient management” of the Old Football Pitches, the result was that they were emptier than before.

The legal position is similarly confused. The Royal Parks agency says it has the legal power to charge for usage when it has not charged before. This is a power incidental it seems to the powers granted under section 22 of the Crown Lands Act 1851. Whilst it is true that the Royal Parks can charge for football and tennis pitches, it is not obvious that this also applies to when people just turn up and play a sport, even if there is a league organised between them. I also asked the Royal Parks which power was relied upon by the company when it threatened in July to summon the police against the charity workers playing in a public park. I was told that this was under regulation 13(a) of the Royal Parks and Other Open Spaces Regulations 1997, which provides that no person using a royal park "shall in contravention of a notice exhibited by order of the Secretary of State, or after having been required by a constable not to do so, play any game or engage in any form of sport or exercise". But was there such a notice issued by the Secretary of State, I asked. Nobody at this executive agency of the DCMS could tell me.

In any case, the law is not on the side of public spaces. As Professor Antonia Layard explained to me, there is actually no legal category of "public space" in English law, just different types of private ownership. There may be some illusion of "public space" but all land is the property of someone, and that person invariably has rights they can enforce against the public using that land, whether that be the crown, a local council, or a private landlord.

Perhaps, in the grand scheme of things, it does not matter to you what happens to the London Charity Softball League. There are other places for them to play, even elsewhere in Hyde Park among the picknickers, dog-walkers and the joggers, even though those areas will be not be as suitable. But these small instances do mount up, and in aggregate the loss is expensive to our civic society.

What is happening at Hyde Park is a micro-example: just one ill-thought through and badly executed sudden “change of policy” which will be enforced by threats of coercion regardless of the practical consequences, even when those consequences are pointed out, just because it will supposedly bring in more money.

And so tonight the charity workers will say goodbye to each other at Hyde Park. They will not be able to afford to play next year. The Royal Parks know this, but they refuse to shift their stance.

Ultimately this is not about softball and charities; it is about all the unknown benefits which will now be lost because of the casual way those with power are restricting the free use of public spaces. As Vanessa Furey, co-ordinator of the campaign against the charges says:

This isn't just about our softball league, it's about all the other small groups who have used this areas for years and have built up a community. If we don't stand up an question this policy, who will? Our league was founded 10 years ago as an chance for people across the charity sector to informally network and look for opportunities to collaborate. In that time it has grown from 9 teams to 68, but without the ability for us all to go to this area in Hyde Park and play for free, it may never have got off the ground. Already this season we've seen fewer and fewer people using the area and a dramatic drop in teams from the league. These charges will not only have an impact on our softball league, but it's a financial barrier which will stop others from creating similar grassroots initiatives.

And it is not just about London. The Open Spaces Society tell us that all over the country spaces which have been or should be freely available for public enjoyment are being closed off, with people excluded unless they are prepared to pay. And it would appear this often done by stealth, without any consultation or advertisment, on an unclear legal basis, and sometimes even against the explicit basis why the land was made open to the public in the first place.

We are already in a country where charity workers can be threatened with the police by a private company for playing softball in a public park; one can only fear what worse micro-examples are to come before it realised there something valuable to us all is becoming lost.

David Allen Green is legal correspondent of the New Statesman