Hi @Crookie - There is a good selection of supermarket brands in the UK.
ALDI and LIDL are the cheapest, both have a smaller variety of each product but you can easily do a full shop in either.
CO-OP and PREMIER tend to be smaller, local and expensive although CO-OP do really good reductions late in the day
SAINSBURY’S, ASDA and TESCO are generally more expensive but have a much wider selection. In the larger of these stores you can buy almost anything aswell as groceries - clothing, hardware,toys, etc
WAITROSE and M&S are the most expensive.
Be aware that most the big supermarkets now also have smaller local convenience stores so Asda ‘local’, Tesco ‘express’ Sainsbury’s ‘metro’ etc will be much smaller and more expensive than the large supermarkets of the same name