Michael Meacher has urged the prime minister to act with caution over the forthcoming decision on whether to commercialise genetically modified crops in the UK.

The former environment minister told MPs there had been no human feeding trials on the effects of GM foods.

"Until these tests are done, one important option for the government in reaching its decision later this year is the exercise of the precautionary principle," Meacher said.

He said it was a principle that should be "very seriously taken on board" by the government.

Before leaving office in last week's reshuffle, Meacher had been pushing for his ministerial colleagues to act with caution on the issue.

Responding, the prime minister said that the decision would be taken on the basis of scientific evidence, "not on the basis of prejudice".

"The biotech industry in this country is an immensely important industry," Tony Blair told the Commons.

"It is important for the future of that industry that they recognise that decisions that government takes are going to be based on proper scientific evidence."

He also expressed concern that there were some in Britain and Europe who "aren't prepared to give enough consideration to the potential benefits, as well as the potential downsides of this".

"All I say is for the future both of our country and other countries it is important this is conducted on proper scientific grounds."