This website, from the Chartered Trading Standards Institute and the Department for Business, Energy and Industrial Strategy, offers "trading standards law explained". It is aimed at businesses primarily, and helpfully distinguishes clearly between the law in Scotland, and elsewhere in the UK.
Citizens Advice Scotland Consumer Service
A good collection of basic advice articles on a number of common consumer problems e.g. car repairs, cancelled flights, switching energy providers etc. It also includes template letters which can be used to make complaints or request refunds in different circumstances.
Competition and Markets Authority (CMA)
This corner of the UK Government’s web presence has a good amount of consumer protection related legal content, including collections of guidance and CMA cases.
European Commission (Justice and Consumers)
Although the United Kingdom has left the European Union, certain pieces of legislation (formally known as 'retained EU law') will still apply until such time as they are replaced by new UK legislation. Therefore, this resource may still be useful regarding consumer and business matters under EU law and policy.
Financial Conduct Authority (FCA)
A really well set out website, this section deals with common consumer issues and provides good jargon-free advice on what to do. Of particular interest is the list of common scams to look out for and avoid!