“And that’s not all,” Amnesty continued, before alleging, “We’ve discovered illegal equipment being advertised.
“At some we found cluster bombs, at others it’s been leg irons, electric shock batons and stun guns – tools used to torture people.
“We think people should know what’s happening on their doorstep.”
Along with the advert, Amnesty has taken out newspaper adverts along with posters placed in locations around London.
More than 1,500 companies will exhibit their goods at the fair.
At past fairs, campaigners claim to have discovered a range of illegal torture equipment advertised for sale, including leg iron restraints, stun guns and cluster weapons.
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A petition to stop the government trading in illegal torture equipment is also on the Amnesty site, reaching more than 18,000 signatures.
Oliver Sprague, Amnesty’s Arms Programme Director, says: “We want to see the end of the UK playing the dirty role of matchmaker between trader and torture.”
DSEI responded by saying: “DSEI fully respects the rights of all individuals and groups to engage in lawful protest, and we have always accommodated a number of such groups that wish to make their views known to our attendees in a peaceful manner – this year is no different.
“DSEI is the world’s largest land, sea and air defence and security exhibition.
“The event provides an effective and well regulated platform for the British defence industry which has a turnover of £30bn and employs 233,400 people directly and over 145,000 people indirectly.
“This year DSEI will play host to a variety of cutting edge technologies ranging from defence systems and equipment designed for British forces, through to equipment that will be used by first responders to natural disasters around the world.
“Ministers from across the UK Government will attend DSEI, meeting British companies and underscoring the important role the defence and security sector plays in the UK.”