More research is needed before widespread commercial production of GM crops is allowed in Britain, a senior government scientist has warned.

Not enough is known about the impact that genetically modified crops may have if they cross-breed with natural varieties, Professor Howard Dalton told BBC News.

We have a responsibility to ensure the experiments are done properly

Professor Howard Dalton

The chief scientific adviser at the Department for Environment, Food and Rural Affairs (Defra) said this was why a precautionary approach was necessary.

"My concern is that we are moving specific genes, often just one at a time, as opposed to the many thousands you do with normal plant breeding.

"What we don't know are the implications of what that one foreign gene might have on other proteins in the recipient plant material," he said.

Defra was liaising with the Food Standards Agency to see what these problems might be, he said.

Possible delays

"They are looking at many of these modified plants to see if they are toxic or dangerous... we don't know what the implications might be because it's not a normal thing to happen.

"I want to make sure that as a result, there are no problems," he said.

He hinted that there might be further delays to commercialisation of GM crops in the UK.

"If there's an extra delay of a couple of months - maybe six months or whatever, of course [the biotech industry] will be frustrated, but at the end of the day it needs to be done and we have to do it.

"We have a responsibility to ensure the experiments are done properly and the results available for everyone to see."