Consumer law states that: With regard to the manufacturer’s warranty that comes with a car when it’s new, Block Exemption allows you to have a car that’s under warranty serviced by an independent garage, provided it adheres to the car maker’s servicing schedule and uses genuine parts.
However, it doesn’t apply to the extended warranties offered by many car makers, so it can be stipulated in the terms and conditions for these, that the car must be serviced by a franchised dealer.