Many thanks for your patience, I am pleased to be able to continue assisting with your query now.
Whilst you may believe it is against your human rights not to wear a mask, it is also the supermarket’s right not to allow you on to their premises without one or not to serve you as a result. Bear in mind that a supermarket is basically private property and they have the right to decide who is allowed on to their premises, just as you have a right to decide who comes into your house.
So if you are not adhering to their rules, or the rules they are following based on what the Government has implemented, it is pretty simple – you will be refused entry and/or service. That is not illegal on their part – they do not owe you anything, they are not obliged to deal with you or sell you anything, even if you believe you are exercising your human rights in the process.
If you comply with their requests peacefully, such as leaving if asked to, then there should be no problem. However, if you kick up a fuss and refuse to leave and demand you are allowed in or served, that is when they can involve the police and you could potentially be fined or cautioned. Don’t worry about jail – that is very unlikely unless there has been something very serious, like a physical assault.