In my experience you won't need employers liability as you are not an employer, you say it's an advisory role. But could the advice you give have an effect on members of the public? 

When we first set up as a consultancy (limited company) we only had professional indemnity and employers liability insurance (we needed EL as there were two of us).  Over the years as we took on more work we were required by the contracts we signed to have public and product liability cover.  In essence these were not always required but if we wanted the the work we needed to get the cover.  Over the last eleven years we have paid out quite a bit for cover and like a lot of companies we never needed to claim.  I guess the point I am making is sometimes we as consultants have to follow the requirements of the people we are going to work (who sometimes make up their own rules) for just to get the work. A case of "who pays the piper calls the tune".