In America they have a name for it: Nature Deficit Disorder. Nature, says the writer Richard Louv, is more important than you think. Divorce nature from your life and bad things will happen. For a start, you become fractious and bored, and unable to concentrate. Then you risk obesity and mental health problems. Nature, continues Louv, is fresh air for the mind. It is the link between life and happiness. But increasingly, it has become a missing link. To more than half of us aged 30 or less, nature is only of marginal interest. Like the girl who, when told there was a wild badger in the garden, glanced up from her ipod and mumbled, "This affects me – how?"

Yet when it comes to public policy, nature is always up there as a big deal. Parks and public gardens are managed with wildlife in mind. And we have never had more freedom to roam. We can go where we like over open hills and downs and commons. Forbidden forests have been thrown open to inspection, and liberally supplied with car parks, loos and picnic tables. The Government is committed to open access all around the coast. We must be the most walker-friendly country in Europe.

So what is amiss? Why the disconnection between access and enjoyment? One reason, of course, is that parents worry that their children might be abducted and abused. Or that they could get run over on our busy roads. Or even, according to social research at Hertfordshire University, that they might get their expensive trainers dirty. Unlike the generation that went through two world wars, we are not inclined to take risks. For many parents and children, the countryside has become off-limits, outside the safety barrier, an uncomfortable place. As Richard Louv puts it, "our society is teaching young people to avoid direct experience with nature".

But there is another barrier to appreciating nature, and it is this: even when you find it, you are not allowed to touch it. Nature used to be associated with freedom, freedom to see and think unstructured thoughts, and to wander as you please. But all too often the nature experience now involves some corralled "country park" or "discovery centre" or guided tours by people who may or may not know much but are usually pretty hot on the dos and don'ts.

I call it the Don't Touch culture. The don'ts include picking or playing games with wild plants, catching pond life or flying insects, foraging for wild food, climbing trees, or burning wood on a campfire. Many people seem to think such activities are illegal. Doubt has even been raised about the legal position of picking blackberries by the wayside. Personal, direct contact with nature is being discouraged by fusspots and busybodies and control freaks who seem to want to regulate every waking moment of our lives. You can read their disapproval in the small print under the welcome sign at the entrance. Look but don't touch. You know it's illegal.

Well, actually it isn't. It is not, for example, against the law to pick wild flowers, though you don't hear many conservation bodies saying so. It is, however, illegal to dig them up. Hence we are in the idiotic situation where gathering the roots of a wayside horseradish or grubbing for pignuts for a wayside nibble, as previous generations did, is committing a crime.

Yet the state never intended it to be like this. It happened in this way: back in the Eighties, after a bit of bother over the sale of wild bluebells and primroses, a law was introduced to make such activities an offence. But to make life easier for the lawyers, it included a blanket clause making it illegal to dig up any wild plant by the roots. Hence, in the eyes of the law, and for no better reason than a tidy statute, weeds and edible roots are protected with the same force as orchids.

Nor is there anything in law to stop you chasing butterflies, other than specially protected ones, or collecting their caterpillars to breed. If there was, high street toy shops might be in trouble when they sell butterfly nets to toddlers.

We can also still forage for winkles and cockles, but as the author of a recent book on wild food noted, the law is a nightmare: "I defy anyone not having a firm and comprehensive grip on the law to collect half a dozen different things from the beach without committing an offence." As for mushrooms, an enforceable Code of Conduct allows us to gather a small basketful so long as we do not sell them on, but some public landowners have been reluctant to allow us even that much.

What matters more than the strict letter of the law is the sense that direct contact – enjoying nature by touching, sniffing, chasing or nibbling – is somehow morally wrong. While we may be within our rights to pick some buttercups for the vase, we may decide not to if it attracts unfriendly whispers and stares, and perhaps a word to some warden or official. Taking a butterfly net to a protected place may be strictly OK, but it marks you out as a potential criminal.

The result is a deepening divide between people and nature, for it makes nature study to all intents and purposes impossible except as an organised activity (supervised by adults, that is). This matters because it is only when you get up close and personal with a plant or insect that it enters your memory and imagination: the distinctive smell of the flowers, the way a dragonfly loops its long body to position an egg, or the patterns a mushroom makes on paper when you leave it overnight. It is through "watching narrowly" that we get to know our fellow beings, and learn their names. Yet how often, these days, do you find people, and especially children, really looking at things?

To seek an example of how this alienation from nature is subtly encouraged, you need look no further than the Oxford Junior Dictionary. Designed to meet the needs of seven-to-nine-year-olds, the latest edition of the dictionary includes such modish words as blog, bullet point, biodegradable, Xbox, chatroom and MP3 player, all of which are deemed to play an important part in the lives of children today. But to make room for them, the editor has excised many of the most familiar objects of the countryside, words such as acorn, conker, dandelion, minnow and magpie.

In proscribing minnows and conkers, the editor claims she is only responding to the needs of contemporary life: "Nowadays most children no longer live in semi-rural environments and see the seasons. The environment has changed." What a thought: children who do not experience the changing seasons, nor will have any name for the things they find on a simple country walk. Small hope there of any budding naturalists. As Kate Humble, the Springwatch presenter, expressed it: "If a child hasn't ever got its hands dirty sifting through soil for bugs, kicked up leaves, or been wowed by a cute baby bird, how can we expect them to care about the natural world?"

How indeed, but what can we do about it? There is no shortage of projects and schemes intended to bridge that gap. Natural England, for instance, not only promotes its own nature reserves as "green gyms" but has also launched a £25m grant scheme to bring nature closer to the lives of "those who face social exclusion or have little or no contact with the natural environment".

But such officious striving, however well-meant, comes across as heavily paternal, if not patronising. By placing terms on how we enjoy nature, by treating it as something apart from ourselves, they are still playing the Don't Touch game. Nature doesn't belong to the planners and conservationists: it's ours. It's our habitat, the place in which we all dwell, whether it is a city centre or a country village.

And, it seems, we also need it, not only for intellectual stimulation but for the basic building blocks of human happiness: the sense of freedom to wander, of wind in your hair, of clouds and stars in the sky, the sounds and feelings of a world beyond everyday cares. How do we break free of the Don't Touch Gestapo?

I suggest that we should press for the re-establishment of a right that once belonged to everyone: the right of forage. At the moment, our ability to collect nuts or berries by the wayside is regulated under the Theft Act, as though we are thieving the rightful property of some lord or squire – a notion that dates back to the Black Acts of the eighteenth century, when you could be hanged or deported for stealing a sheep.

Those nuts and berries are rightfully ours. A right of forage would establish that every wanderer along the public highway can pick or collect the products of nature on the premise that such things are not privately owned but held in common. We would, if we chose, be able to pick common wayside flowers, gather wild nuts, berries, mushrooms for the pot, and take home interesting bits of dead wood or fossils. We could capture caterpillars and tadpoles, build wigwams out of fallen wood, and play games with elder stems or plantain guns. The wildlife can take it. And we would become freer, happier, and in the long run, more aware of the plight of nature and ourselves in a perilous and rapidly changing world.