You may be a tradesman and when you go to do a job they may insist that you have
Public Liability Insurance and that you have it before you start the job and in many cases you have to show them that before you will be able to get paid. Although Public Liability Insurance is not a legally compulsory insurance more and more people are insisting that you have to have it if you want to do any work for them as they want you to be covered should anything happen during the course of your work.
The other area of this is Employers Liability Insurance and this is a lot easier to understand whether or not you need it as it is a legally required insurance. If you employ anyone directly or as a labour only sub contractor then you must have this insurance by law and there are penalties for companies that are found without this insurance which can be anything from a fine or a ban on running a company up to something much more drastic like imprisonment.
The main thing that most people get confused is what each of the above insurances actually covers so I will try to explain exactly what you need the above for. Public Liability Insurance is used to cover you for any case of 3rd Party accident or injury that you may cause in the course of your days work. For example if as you were entering a property you knocked over an expensive vase or if you left your tools lying around and someone was to trip over them and hold you responsible then this is where your Public Liability Insurance would come in to play.
The Employers Liability Insurance is slightly different and is to provide cover for injury, illness or death to anyone you employ (either directly or as a labour only sub-contractor). For example if you were in the painting and decorating industry and one of your employees was working on a ladder you supplied them with which then collapsed causing them to fall and injure themselves then they may hold you liable. This type of insurance differs from public liability insurance which would provide cover for injury or property damage you cause to a member of the public during the course of your occupation; usually you cannot get employers liability without having public liability.
So if you are working on your own as a sole proprietor then you can decide whether or not you want to get Public Liability Insurance (but be aware that some people will still require that you have it before you can do a job for them) but if you employ anyone then you must get Employers Liability Insurance.