The answer to this question is that it depends on the specifics of the business/trade that you are carrying on and your appetite for risk. For instance are you operating from your own premises, working on site, designing and making etc?
if you employ anyone you will need employers liability insurance.
Public Liability and Product Liability insurance are not the same thing although are commonly packaged into a combined liability type policy by insurers.
I would suggest getting proper advice either by speaking to insurers yourself or an insurance broker.