The Royal Institute of Chartered Surveyors (RICS) called for the creation of a land register through which potential buyers, and banks, could find out if and when GM crops had been planted or grown on a particular holding.
In a separate move, the Government announced that the independent advisory group on planting of GM crops will investigate the effects on British wildlife and biodiversity of commercial growing.
Lord Whitty, the environment minister, said that the remit of the Advisory Committee on Releases to the Environment (Acre) has been expanded, and a subgroup set up to examine biodiversity issues. "With these regulations in force, British wildlife species should be protected against effects from the commercial use of GM crops," he said in a Lords' written reply.
However, the RICS report, sent to the Government's Office of Science and Technology and other departments, warned that growing such crops might lower the value of the land. In the case of tenant farmers, a landlord could, in effect, sue for any shortfall in land value caused by the tenant growing GM crops.
Michael Chambers, director of the RICS's policy unit, said that if commercial growing goes ahead, it would require a permanent register of sites where GM crops were or had been. "It's very hard to see how it could be controlled once you grow on a widespread scale in the countryside," he added.