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Nicotine, found in tobacco, is a deadly substance – and not only for smokers. It has long been known as a powerful natural insecticide, and its presence in the tobacco crop has evolved to deter pests; it is toxic to virtually all of them (except one, the Carolina sphinx moth, whose fat green caterpillar, known in the US as the tobacco hornworm, has evolved a way of dealing with it).

Nicotine is a neurotoxin, that is, it attacks the insect nervous system. In recent years, pesticide companies such as the German giant Bayer have developed a group of compounds which act in a similar way; they have been christened neonicotinoids ("new nicotine-like things"). Neonicotinoids are now among the most widely-used insecticides because they are very effective, and they are effective because they are "systemic". That means that they do not simply sit on the plant's surface but are taken up into the plant itself, so that any part of it becomes toxic to the aphid or other troublesome wee beastie attempting to feed upon it.

Unfortunately, when we say "any part", that is literally true: not only the stem and the leaves are contaminated but so, even at the heart of the plant's flowers, are its pollen and its nectar. And when pollinating insects come along to gather them, such as honeybees, bumblebees, solitary bees, moths, butterflies, or hoverflies, which are by no means the "target" species of the insecticide, they get a shot of poison nonetheless. They may get a tiny shot. But each time they buzz to a contaminated flower for more pollen or nectar, they get another one. And another one. And another one.

In the great mysterious crash of bee populations, which has been gathering speed around the world for the past decade or so, and which has started to alarm even governments because of the vast worth of bee pollination to the agricultural economy (more than £12bn annually just in Europe), neonicotinoids are increasingly suspect. In the great crash of other insect populations which has similarly been taking place, about which governments do not give a toss but which nonetheless threatens the natural environment with catastrophe (many insectivorous birds are dropping dramatically in numbers), neonicotinoids are similarly in the frame.

For they do not only pose problems through pollination. Neonicotinoids persist in the soil and have high leaching potential, meaning that they can not only harm soil organisms but can be washed out and end up contaminating water bodies, and they may be implicated in the enormous decline in aquatic insects such as mayflies which we have seen in recent years.

So how can such pesticides be licensed for use? In European countries, the initial licensing is done at European Union level by way of a Draft Assessment Report (DAR); but although the basic research for it is usually done by independent scientists, the organisation of the report – remarkably, you may think – is carried out by the manufacturer. So the DAR for the commonest neonicotinoid, which is called imidacloprid, was put together by Bayer, which makes imidacloprid, and which makes many millions of pounds from it every year. And guess what? Bayer's report found no reason why it should not be approved!

Fifteen months ago, however, the British invertebrate conservation charity Buglife conducted a review of all the available scientific literature about the effects of neonicotinoids, and imidacloprid in particular, on non-target insect species; this produced a much more troubling picture. Referring directly to 100 independent, peer-reviewed scientific papers, the Buglife study highlighted a raft of concerns that neonicotinoids are indeed harmful for bees and other pollinating insects, especially chronically (that is, through tiny doses ingested from repeated visits to contaminated flowers) – something which the testing methodology of the imidacloprid DAR, the Buglife study said, simply did not pick up.

These concerns have become widely shared, at the national level – France, Germany, Italy and Slovenia have all banned neonicotinoids to a greater or lesser degree – and they have been further heightened by the recent leak of a confidential internal memo from the US Environmental Protection Agency, which warned that bees and other insects were at risk from another Bayer-produced neonicotinoid, currently on the market, called clothianidin.

The British response? Zero. At present, despite the concerns, about 30 products containing imidacloprid are cheerfully licensed for use on British farms and in British gardens. But then the British government, especially the present one, is very relaxed about pesticides, as was made clear by the junior environment minister, Lord Henley, in his response before Christmas to new EU legislation on sustainable pesticide use. He could have brought in various improvements on the back of it, such as a ban on pesticides near schools, playgrounds or hospitals, or a mandatory requirement to notify communities before pesticide spraying which might affect them. He chose to do nothing.

Yet many might think that applying substantial doses of poison to the landscape is hardly an issue to be relaxed about: get it wrong and the consequences are horrendous. Rachel Carson first showed us that 50 years ago next year when she published Silent Spring, the book which, in documenting the terrible toll pesticides were taking on American wildlife, effectively launched the modern environment movement. Carson's concern then was organochlorine substances, principally DDT. But looking at neonicotinoids, and the mounting evidence against them, and the persistence of their use, the thought is overwhelming: have we learned nothing in 50 years? Carson feared a world without birdsong; and here we are fearing a world without bees, half a century on.