//bob, shops are only supposed to sell essential items, e.g food etc.//
Here we go again. Misunderstanding of the legislation rears its ugly head.
Diddley is quite correct. Leaving aside the difficulty in determining what is "essential" and what is not, shoppers are not restricted to buying essential items and shops are not restricted to selling them. The legislation states this as one of the "reasonable excuses" for leaving home:
" (a) to buy goods or obtain services from any business or service listed in Part 3 of this Schedule,"
So what the shop sells is not the issue. It is whether it is allowed to open and if it is it can sell what it likes and shoppers can buy what they like from them.
If there is any conspiracy in this whole affair it is that formed by the authorities, the media and the police when they conflate the law with the guidance or even just with a "recommendation." To be fair, on this issue (unlike the "exercising" allowance) there has never been any misleading information within the government's official guidance. It simply says "You can leave home to buy things at shops or obtain services." So quite where this idea that you can only buy "essential" goods comes from, I don't know. It might have come about from the occasion when the police (Staffordshire, I think) began rummaging through shoppers goods to ensure they had only bought essential items. They were swiftly admonished and the practice stopped, but obviously some people believed what they were doing was within the law.
No doubt there will be some people who believe those police were perfectly justified in their action and would like to see more of it. My response is the same - police must act within the law and not make up their own rules.