The planned appeal by the four men convicted of a failed bomb plot hinges on whether the home-made explosives they were carrying were viable.
All four men claim that the plot was an elaborate hoax and that they never intended carry out a bombing.
However, the Forensic Explosives Laboratory (FEL), a top security government facility which tested the devices, concluded that they would have worked had the chemical recipe been correct.
It is this conclusion that will be called into question if the men file appeal papers.
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