The formal park of Dunham Massey in Cheshire is among the most magnificent in northern England. It was laid out by Lord Warrington in the late 17th century with 100,000 trees, possibly the most ever, justified explicitly as "for the benefit of posterity". Posterity duly benefited. The park grew, and by 1843 the new canal from Manchester was bringing Whitsuntide trippers by the tens of thousand to wander Dunham's groves and breathe its fresh air. It was Manchester's lung - and under the custodianship of the National Trust still is.

On New Year's Day 2005, one of Dunham's mighty 260-year-old beeches was hit by a sudden, 67mph gust of wind. It fell on to its neighbour, which in turn toppled and killed an eight-year-old boy. It was an accident, and nobody pretended otherwise. The Health and Safety Executive, in league with the police, arrested and cautioned the property manager for possible manslaughter, but the police dropped the case for lack of evidence after a year.

The HSE did not do so. What used to be called an act of God has, since the invention of the HSE, been redefined as an act of man. There is no longer any such thing as an accident, or lawyers would starve. The chance of a tree killing a person in Britain is infinitesimal. There are barely half a dozen deaths a year attributed to trees, usually in cars driving into fallen ones. For a tree to topple on to a person, the odds are about 25m to one.

The HSE is none the less continuing its inquiry, to pin a case on the National Trust for criminal negligence under the Health and Safety at Work Act. The crime, presumably, is neglectful ownership of any tree that might fall over in a high wind. If the Trust can be found guilty, lawyers for the bereaved family may sue it in the civil courts for damages. The cost in litigation alone will be enormous.

The case has traumatised the National Trust and its park staff nationwide. They are responsible for 6m trees under which millions of human beings wander daily. Should they chop down every old tree, or only some, or close all treed areas to the public? Nobody knows. The case applies to all landowners in the public domain, which under the right to roam could rise to billions of trees.

When Trust staff are asked what most concerns them, they no longer cite lack of money or visitor numbers or interfering management. They cite the HSE. This body, with its terrorising inspectors, its box-ticking approach to safety, and its agents enforcing its edicts to the letter, is feared and loathed with equal passion.

The HSE naturally objects to being seen as the stormtrooper of "health and safety fascism". It constantly points out that 212 people die each year in industrial accidents (against 2,300 outside its remit on the roads). Its mantra is that any death is one too many, that nothing can be too safe. Any risk is a threat. The HSE is the Guantánamo Bay of defensive administration.

The litany of activities on which the HSE has declared war is familiar. The latest victory, against Cathedral Camps for volunteers repairing churches, reflects the HSE's long campaign against old buildings. Its ban on ladders, used since the middle ages to repair roofs and steeples, must have quintupled the cost of maintenance. I have visited towers closed, spiral stairs bricked up, ponds drained, walls banned and ruins barred in the name of the HSE. This month its agents stopped our local Guy Fawkes bonfire and firework display, held without harm for decades. No explanation was given, merely that "the minister" had banned it.

The HSE often shelters behind public outcry over any publicised deaths where "something must be done". Yet there was no outcry over Dunham. This body operates beyond the realm of government and can sue on its own behalf. Its accountability is to a minister, Lord Hunt, who is not even in the House of Commons. Three years ago it took the then commissioner of the Metropolitan police, Lord Stevens, to the Old Bailey following the death of a constable chasing a crook. Its complaint was that he had given the constable "insufficient training" to keep him off a dangerous roof. It lost this ludicrous case, but was unrepentant. It now wants the National Trust as a feather in its cap.

Defying the HSE is near impossible because behind every case is an ambulance-chasing lawyer ready to pounce. Disobeying the HSE is prima facie "negligence", and will be treated by the ever-indulgent courts as such. This encourages the no-win, no-fee firms that advertise widely on radio and television. No one - not the HSE, the lawyers or the safety suppliers - has an interest in reducing this nonsense. Health and safety is an industry.

Occasional bleats of protest are heard. One impotent old-timer, Tony Blair, remarked earlier this year that "in my view, we are in danger of having a wholly disproportionate attitude to the risks we should expect to run as a normal part of life. This is putting pressure on policy-making, not just in government but in regulatory bodies, local government, public services, private sector." He did nothing about it.

Last month, something called the Better Regulation Commission produced a report citing lunacy after lunacy imposed by regulators in the fields of transport, housing, health and food, as well as the HSE itself. It even called for a new body to regulate the regulations. Yet, as anyone knows who runs a farm, shop, restaurant, entertainment venue or rental property, safety is no longer a sensible concern for one's staff and customers, but a raging disease of the state.

Occasionally the HSE protests that it too is human. Like Frankenstein, it howls that the monster it has created has escaped control. Last year its chairman, Bill Callaghan, declared himself "sick and tired of being accused of stopping people doing worthwhile and enjoyable things" (like lighting my bonfire or walking freely on my local jetty?). He said everyone should take a few risks after all and, as he put it, "get a life".

An HSE document even suggested a rule of thumb, that "an individual risk of death of one in a million per annum for both workers and the public corresponds to a very low level of risk, and should be used as guideline". Why then is Callaghan persecuting the National Trust for a risk that was one in 25m?

The HSE is like the Child Support Agency, the Criminal Records Bureau and the Rural Payments Agency, a state body whose introverted culture has polluted its own reason. Why should no seats be allowed at open-air concerts? Why should swimming-pool diving boards be banned? Why should people not walk under old trees? Can people never be allowed to make such decisions for themselves?

This is the product not just of bad government but of too much government, addicted to bossiness, crazed by control, and careless of the misery it brings to good citizens trying to help others. It is mad, and nobody seems able to stop it.