Protesters have vandalised a genetically-modified crop site near Tadcaster - but the land did not contain "Frankenstein food", it was revealed today.

Police are investigating the attack, which was carried out under the cover of darkness at Headley Hall, a farm leased by the National Institute of Agricultural Botany (NIAB) for trials of GM oilseed rape and sugar beet.

The protesters scythed and beat down the 3ft high oilseed rape before trampling it into the soil.

It is the second time the farm, which belongs to the University of Leeds, has been targeted - and both times the attackers have got it wrong.

In yesterday's incident, the 100-square-metre experimental site contained a "control" crop, which is used for comparison purposes and has not been interfered with genetically.

And in the first attack on the farm last August, a potato crop which was destroyed turned out to be GM-free.

On that occasion, a fax was received by the University of Leeds from an activist group which claimed responsibility and threatened to return.

The trials are being conducted by the NIAB to check whether the strains meet safety standards with a view to using them commercially in the food chain.

Vanessa Bridge, chief press officer at the University of Leeds, said today the GM oilseed rape had already been removed when the site was vandalised yesterday.

She said: "The oilseed rape is about three feet high at present. They came just after midnight and apparently used scythes and sticks to cut and beat down the crop."

NIAB's regional manager, Neil Pearson, who is in charge of the Tadcaster trials, said: "We have suffered an act of vandalism involving oilseed rape, which was discovered yesterday morning.

"It's a sensitive issue and I am unable to make any further comment."

Andrew Waller, Friends of the Earth co-ordinator for York and Ryedale, said: "This latest attack doesn't surprise me, but we don't condone vandalism.

"We support a five-year freeze on the commercial planting of GM crops because their potential dangers to human health and hybridisation of weeds haven't been fully explored.

The NIAB says if GM crops were to be grown on a commercial basis, they had to be cleared by the whole European Community.

It also argues that GM cheese and tomato paste are already on supermarket shelves.

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