The UK Government's chief scientist says he is concerned about the possible effect of genetically modified (GM) crops on wildlife.
By Alex Kirby
BBC News Online environment correspondent
The scientist, Professor Sir David King, chairs the government's GM Science Review Panel.
Sir David told BBC News Online that precaution should govern the discussion on whether to grow GM crops in the UK.
In the meantime, he said, the moratorium on planting them should stay in place.
The panel's report says GM crops pose a very low risk to human health, but expresses doubts about their possible impact on the wider environment, especially wildlife.
One passage reads: "We do not yet have sufficient evidence to predict what the long-term impacts of GM herbicide-tolerant crops would be on weed populations and the wildlife that depends on weeds for food.
"Above all other concerns, this poses perhaps the most serious potential harm arising from these particular crops."
Dr Mark Avery, director of conservation at the Royal Society for the Protection of Birds (RSPB), is a member of the panel.
He said: "The RSPB has been warning for five years that the commercial release of GM herbicide-tolerant crops could make a bad situation for farmland wildlife even worse.
"This report shows that eminent scientists as well as environmental organisations fear GM cultivation will adversely affect wildlife."
One at a time
Sir David told BBC News Online the panel's report was "neither a green light nor a red light to GM crops per se".
He said: "What we are stressing is that we can move ahead if we take it on a case-by-case basis.
Wildlife needs weeds and stubble
"If there is any key important message to come through this report, it would be: 'Let's not talk about the technology in general, let's take each specific case of a product produced by it and see how the product behaves.'"
Asked whether the absence of a green light for GM crops in general did not mean that precaution should be the watchword, Sir David replied: "Yes. I don't disagree with that at all.
"We're not moving away from the precautionary principle in our report. We have to worry about biodiversity and GMs' effect on it.
"We also have to worry about the consequences of gene transfer. We have a diverse agricultural practice in this country - organic farming, conventional farming, and now the potential for GM crop farming.
"Biodiversity is very much an issue of concern to the public, and to us. This is precisely why we haven't in this report given a firm green light at this stage.
"What we're saying is more research needs to be done, in particular on this issue of biodiversity in relation to the current generation of GM crops.
"So we're not recommending that the moratorium on the British planting of GM crops should be lifted at this stage. We do not have the information in relation to biodiversity."