Possible Clues:

• Restrictive association
• Group of firms that agree fixed prices to limit competition
• Group enjoying Monopoly caught playing later
• Claret (anag)
• Time in custody initially linked to those involved in a bit of a fix
• Manufacturer's association restricting competition
• Market-fixing organisation
• Group that agrees fixed prices to limit competition
• Manufacturers' association keeping up prices
• Syndicate formed to restrict competition