Have you tried Chris Knott, they are traders on here and give forum discount.
As for Gap insurance.;
GAP insurance is additional car insurance you can get that covers amounts not covered by typical auto insurance providers. For example, when you purchase a car, its value automatically starts to decrease. If you get in an accident where the car is totaled, the insurance company will only pay the current book value of the car. However, you might owe more than the current value, leaving you with a few thousand pounds to cover on your own. GAP insurance will cover the remaining amount you owe.
Not a big fan.