The trial of seven Britons accused of plotting bomb attacks opened in London on Tuesday with the chief prosecutor saying Canadian Mohammed Momin Khawaja played a "vital role" in the plot.

David Waters said six of the accused – as well as Khawaja – travelled to Pakistan for training in how to make explosives.

The Britons also smuggled chemicals used for bomb-making back into Britain, Waters said. They were in the final stages of planning an attack, he added.

Mohammed Momin Khawaja (shown after his arrest in 2004) awaits his Canadian trial for alleged links to terrorist activity in Britain. (CP file photo)

Khawaja and the Britons were arrested in March 2004. The allegations centre on a plot to blow up Britain's electricity supply network, as well as trains, pubs and nightclubs. The Britons have pleaded not guilty.

The charges aren't related to last summer's London transit bombings which killed 56 people.

Khawaja, 26, awaits trial in Ottawa on terrorism charges after being arrested at his home two years ago. He has not been named in any offence in the United Kingdom, so is not on trial in Britain. However, he is named as a co-conspirator.

Several of the accused are alleged to have links to al-Qaeda. They're also accused of planning a bombing campaign against civilians to punish Britain for its support for the United States.

Prosecutor alleges accused targeted the public

On Tuesday, the seven Britons, dressed in suits and ties, sat in a glass box in London's Old Bailey court. They were accompanied by their 15 lawyers and surrounded by 11 security guards.

Three of the men are charged with possession of half a ton of ammonium nitrate fertilizer, which can be used as an explosive. Their aim, Waters said, was simple: to cause an explosion and kill or injure British citizens probably in a pub, club or train.

Khawaja is the first person charged in Canada under the post-Sept. 11, anti-terrorism law. He is accused of participating in the activities of a terrorist group and facilitating a terrorist activity.

His Canadian lawyer, Lawrence Greenspon, says it's unclear how the outcome of the British trial may affect the case against his client, whose trial is expected to start in January.

"Well, a conviction obviously wouldn't be good," said Greenspon.

"An acquittal would certainly help, but I don't see a conviction as being a determinant of anything here in Canada."

The judge in the British trial told the court it would take several months for the case to be heard. It is expected to wrap up before Khawaja goes on trial.