He has to declare his commision on the sale to you, it should either be on something he has given you or on the quote from the insurance company. There is no set rate, rates provided by insurance companies vary as do the rates within each company to each adviser, it depends on how much business tthe IFA does overall and what they have negotiated and can consist of initial commmision (a one off payment) and/or trail commision (a fee they get every month or year that the policy is in force).
If they have not supplied you with this they are in breach of the FSA disclosure rules.