Police investigating the sale of suspected fake bomb detectors to countries including Iraq have searched premises linked to three businesses.
Sites raided were linked to Global Tech, of Kent, Grosvenor Scientific, in Devon, and Scandec, of Nottingham.
Cash and hundreds of the devices have been seized, and a number of people are due to be interviewed under caution on suspicion of fraud.
The boss of another firm that sold detectors remains on police bail.
Jim McCormick, 53, of ATSC Ltd in Sparkford, Somerset, was originally arrested in January on suspicion of fraud by misrepresentation.
A BBC Newsnight investigation alleged that millions of pounds worth of the company's ADE-651 detectors sold to Iraq did not work.
The UK government banned the export of the ADE-651 device to Iraq and Afghanistan earlier this year, saying tests showed the equipment was "not suitable for bomb detection".
There are concerns that the hand-held detectors have failed to stop bomb attacks that have killed hundreds of people.
It has since emerged that other bomb detectors remain on the market.
Officers from City of London Police's Overseas Anti-Corruption Unit (OACU) carried out five search warrants on three homes and two business premises on Tuesday.
The unit is investigating whether the devices' abilities have been fraudulently misrepresented, and whether sales overseas are linked to bribes.
OACU head Det Supt Colin Cowan said: "We are concerned that these items present a real physical threat to anyone who may rely on such a device for protection.
"It is for this reason that we are seeking to raise awareness of this threat and obtain assistance from the public."
Police appealed for anyone with information about the devices' manufacture, sale or distribution to call 020 7601 6969 or e-mail OACU@cityoflondon.police.uk