Conflicting Information from Tour Operator

I have received conflicting information regarding the 144 Hour Visa Exempt from British Airways/British Foreign Office/Celebrity Cruises/My Tour Operator regarding whether or not the 144 hour free transit even exists. I hold a UK Passport and will be travelling by AIR from UK to Shanghai Pudong, staying 2 days in Shanghai, then departing by SEA from Shanghai Cruise Port onward to Japan. As far as I understand, I am covered by this. Any advice on this would be most helpful.
Many Thanks