Public liability insurance for advertising is available at reasonable prices. Policies can cover your legal liability in the event of injury to a client during the course of your work or property damage due to your negligence. While public liability insurance is not compulsory at this moment in time it is very much advised that you have a policy in place as part of your business plan to cover yourself should anything happen.
Employers liability insurance is legally required if you have any employees, regardless of how often they work. You can obtain a quotation for employers liability covering advertising at the same time as obtaining a quote for public liability. You may want to check the price for future reference in case you are considering hiring staff in the future.