Public Liability insurance is often spoken about in the same breath as Professional Indemnity (PI & PL) but they are separate types of insurance, though similar, and may be jointly covered. Public Liability Insurance protects against claims relating to personal injury or property damage, unrelated to usage of your motor vehicle.
Professional Indemnity is to protect business owners, freelancers and the self-employed if clients claims of negligent acts or omissions. Any organisation which provides a professional service or gives advice could be sued if the recipient is unhappy with their work.
Often PI & PL is offered as an add-on policy, like Gap insurance. As with all insurances, you should make direct comparisons on how much cover you have and if it is aggregate or shared cover (ADI NJC, DIA & MSA, for example, have a shared pot - once it’s gone, it’s gone) or exclusive to you.