Secret film of a suspected terrorist inspecting fertiliser, alleged to be part of a bomb plot, was shown to the Old Bailey yesterday.

Omar Khyam walked round the container of ammonium nitrate then spent two minutes marking the bag because he feared it might be tampered with, the jury was told.

Khyam is seen looking into the bag and bending to mark the point where the powder came up to in the bag, according to the prosecution.

The court was told police and secret services had been watching Khyam and others suspected of being part of a British al-Qaida cell.

Unknown to Khyam, they had already replaced the volatile fertiliser with a safe substance.

Workers at Access Storage in Hanwell, west London, where the fertiliser was stored, alerted police after becoming suspicious, the court heard.

Khyam and a number of others were arrested two weeks later for allegedly plotting to blow up energy utilities, railways and the Ministry of Sound nightclub in London.

Khyam, 24, his brother Shujah Mahmood, 19, Waheed Mahmood, 34, and Jawad Akbar, 22, all from Crawley, Salahuddin Amin, 31, from Luton, Beds, Anthony Garcia, 23, of Ilford, east London, and Nabeel Hussain, 21, of Horley near Gatwick, deny conspiring to cause explosions likely to endanger life between January 1, 2003 and March 31, 2004.

Khyam, Garcia and Hussain also deny a charge under the Terrorism Act of possessing 600kg (1,300lb) of ammonium nitrate fertiliser for terrorism.

Khyam and Shujah Mahmood further deny possessing aluminium powder for terrorism.

The trial continues today.