Ive been saying this for years! It only takes a few minutes on confused.com playing with your estimate to see what difference things makes.
For example, try adding the 85 year old Granny who lives 3 doors away down your road to your quote as a named driver. It will reduce the premium. Amazing really that insurance companies think 85 year old Ethel is likely to be a safer driver in a 300bhp zed than you are.
I did this a few years back now, I put my 74 year old nan on my policy for the first year I owned my zed, it took off £300 from the premium even though she struggles with her Clio.
If there's a loophole there then exploit it because if the insurance company can find a way to get out of paying out for you they will!