Getting a pass plus certificate can help reduce your insurance costs a bit, and it's a lot cheaper than a full blown advanced driving qualification. You might get cheaper insurance from places that specifically insure new drivers, like Ingenie or Marmelade.
Also, as IWMTom pointed out, you're looking at some very powerful cars for a new driver (which you almost certainly are, unless you've been driving since before you were seventeen). Anything over a one point four is going to be very, very expensive. I would be surprised if anybody offered to insure you for less than six thousand pounds a year (especially on a BMW. They're infamous for being driven badly).
Don't lie to your insurers, because if you get found out it's fraud (and it means that the car technically isn't insured, so it could be impounded and the driver can get six points and a fine). I don't know enough about the insurance brokers to comment, but that definitely does sound dodgy.