Baroness Young, the Labour peer who chairs the organisation, told MPs that several generations of crops had to be grown before the cumulative effects on wildlife and plants could be assessed.
English Nature caused Tony Blair intense embarrassment earlier this year when it opposed the Government's refusal to impose a moratorium on GM releases.
Baroness Young told the Commons Environmental Audit Select Committee that a ban until 2003 would allow more research on results of field trials.
She said the trials should be "rigorous" enough to take into account broader ecological and environmental implications of commercial releases.
Dr Keith Duff, English Nature's chief scientist, told the committee that management of the field trials was just as important as the growing itself.