Security has been increased around a farm in Hertfordshire where Genetically Modified wheat is being grown.
Campaigners planning to protest about the potential dangers of the experimental crops are being kept away from the crop at the Rothamsted Research centre.
Anti GM group "Take the Flour Back" is worried about contamination to the surrounding area. Rothamsted Research says the possibility of contamination from pollen blown in the wind is small.
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Scotland Yard said two murder investigations have been launched following the separate incidents, which both happened in the past week.
Photos show the extraordinary surgical procedures to remove the growth.
The Met Police says 143 firearms have been handed in at stations across the capital in just seven days, including two antique machine guns.