Do you remember John Wyndham's book The Day of the Triffids? It was a hair-raising vision of a world terrorised by monster, alien plants.

The potential of genetically-modified organisms (GMOs) to turn our world upside down is much less dramatic than that. But many people, including some scientists, believe there are risks associated with genetic engineering that are not worth taking.

They worry about what might happen if new genes introduced into crops from other organisms "escaped" to the wider environment.

A crop is modified by genetic engineers to give it specific, new characteristics - to make it resistant to insect attack, for example.

But environmentalists fear such characteristics could spread, uncontrollably, through cross-pollination, to wild plant varieties with unforeseen and damaging consequences.

We have already seen how the intensive farming practices of the last few decades have made the countryside a pretty hostile place for wildlife.

Agrochemical use

English Nature, the government's wildlife adviser, says there is "strong evidence that a major factor" in the steep decline over the last two decades of 10 farmland bird species - including the skylark - is the result of the increasing use and effectiveness of pesticides.

It has told the government that we must be sure that the new GM technology does not add to the problems that already exist.

But this is precisely what the green lobby fear will happen. If a plant becomes resistant to insects, they say, those insects which once fed on the "old version" of the crop will go elsewhere - and so will the other creatures that fed on those insects. Slowly, but surely, you are driven into a downward cycle of species loss.

English Nature wants research to be given sufficient time for the full effects of GM crops on the environment to be established.

It is vital that we make the right call - particularly on the global scale.

Continued and rapid population growth over the next 50 years will lead to increasing urbanisation.

Climate change

The last remaining areas of uncultivated land will come under intense pressure - not just from the spread of towns and cities, but from the need to grow more food.

The strain on the natural environment will be huge - and the worst predictions for climate change could make the situation utterly intolerable.

But the genetic engineers believe the new, emerging technology will help us to square this circle. As much as 40% of world's agricultural production is lost due to weed growth, pests and diseases. Crops that are modified to tackle these problems could cut out much of the waste.

The technology could allow us to boost yields in a way that is just not possible through conventional breeding and cultivation. We might be able to grow more crops on poorer quality soils and in areas where the temperatures or rainfall have made agriculture difficult in the past. Crops altered to have longer shelf-lives would also help to cut out waste.

This is a scenario in which the environment is better off. Where the new specialised agrochemicals are used less frequently, and those that are put on the land degrade quickly and do not leach so easily into streams and rivers.

On some of the highly efficient European farms, it might even be possible to take land out of production - to return it to "natural" pasture or woodland.