Defo illegal for shoei to insist that a retail price is maintained,I can tell you that from my work experience. Also if a customer has an account with a supplier,and they keep to the terms and conditions of having an account,then a supplier cannot lawfully close the account too,shame not enough businesses know the rules.
But there's nothing to stop them adjusting their wholesale price to outlets, thereby forcing them to comply or bail out...
I'm not so sure,it would stand to reason that the outlets that sell the most units are probably offering very keen retail prices,therefore it would not make sense that a supplier could increase the unit price as say a lesser customer,the OFT would not take kindly.For the t&c to be changed the customer really has to do something wrong like being late with payments,then the supplier can do what they want,even close the account straight away quite legally.Hence discounters make sure they stay within the terms and conditions .