Customers buying 'mixed-use' policies, which cover them for both commercial and private purposes, will be classified as retail customers by the FSA.
For example, a driving instructor buying motor insurance that also covers them for personal use will be considered a retail customer and, as such, the FSA requires that they are given more information than commercial customers.
Royal & SunAlliance FSMA programme director Blyth Morris said: "There is an awful lot of business like that in the market."
He said existing mixed-use business posed the biggest problem as most of it sits within brokers' and insurers' commercial books and was not identified as mixed-use.
An FSA spokeswoman said the definitions were clear: "If you are an individual taking out a mixed policy then you are considered a retail customer. If you are a company taking out a mixed policy then you are considered to be a commercial customer."