I fear you may be mistaken. Below is an extract from an open letter published by the UK Competition and Markets Authority on 20 June 2017 headed "Restricting resale prices: an open letter to suppliers and resellers"
"If you are a reseller:
• You are entitled to set the price of the products you sell, whether online or
through other sales channels.
• Suppliers are not usually allowed to dictate the prices at which you sell or at
which you advertise their products online.
• If you have agreed to sell at fixed or minimum prices with your supplier, you may
both be found to be breaking competition law.
• If a supplier asks you to comply with a restrictive pricing policy you should report
this to the CMA."
Now, admittedly, this is usually applicable to minimum pricing agreements. but I would suggest it can also be applied to open/market pricing. As such, I believe there is nothing illegal in charging above MSRP and wouldn't expect Trading Standards to do anything as no laws or regulations have been broken.