With regards to Business insurance, there's multiple factors that can affect the price.
Age, location, car, business and personal mileage, occupation, the level of cover, type of business use, named drivers, claims and convictions from the last 5 years.
Each underwriter have different rating factors that can affect the overall price.
Contact your current insurer and get them to quote you with business mileage. Don't just estimate what your business mileage is, calculate to the closest mile if possible. You also need to consider what type of business use you require.
Some companies provide,
Class one - SDP and business use for you only.
Joint - SDP and business use for yourself and a spouse
Class two - SDP and business use for yourself and any named driver.
Use a comparison site to get a rough idea of what it could be and haggle with your insurance company if they quote to high.
HTH x