The protesters included Anglicans, Buddhists, Catholics, Jews, Muslims, Sufis and Quakers. They gathered to pray against what they believe is a promotion of violence.
The Defence and Security Equipment International (DSEI) arms fair is setting up this week and will bring over 1600 exhibitors together with military delegations from around the world. The guest list for DSEI includes military delegations from 67 countries.
Other counties include Saudi Arabia, Uzbekistan, Philippines, Egypt, United Arab Emirates, Hong Kong, Turkey and Bahrain which have been criticised for human rights abuses.
According to Rev Matt Harbage, who's also taking part in the protest, all delegations have been invited by the UK Government.
A spokesperson for the No Faith in War campaign said: "The major world faiths share in common a deep sense of the value of peace in the world: a peace which is achieved not by the use of weapons or threats of violence but by dialogue, respect for the dignity and human rights of all and just social structures."
The protesters have received the support of the former Archbishop of Canterbury, Rowan Williams, who said in a statement: "The way much of the arms trade currently works continues to be a blot on the global moral landscape. Governments have been negligent or collusive about the role played by arms exports in sustaining brutal and even genocidal conflicts, and the recent court judgement about arms exports to Saudi Arabia has highlighted the issue."
He said he welcomed the efforts of the protesters to alert people about the unethical cost of trading "weapons of death and mutilation".
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