I'm arriving in Shanghai by cruise ship staying for 48 hrs do I need a visa I hold a U.K. Passport

If you will go to a third country or region rather than the last one you come from after staying in Shanghai, you may be able to enjoy the 144 hour free transit there. No visa will be needed then. However, you are advised to double check that with the cruise ship company if you enter and exit by the same cruise ship.