London to Shanghai then cruise from Shanghai to Japan

Yes, you are eligible if your itinerary fulfills the following two conditions:

- Your flight from London to Shanghai is not allowed to have any additional landing within mainland China and in Japan.
- Your cruise is not allowed to have its first port of call, immediately after Shanghai, in mainland China

If the above two conditions are fulfilled, you are definitely eligible for 144 hour visa free transit and you don't need any kind of visa.

Please, keep in mind to print out your cruise ticket and also a confirmation of your accommodation booking in Shanghai. You should bring these two printouts with you.

Upon arrival in Shanghai, you will approach 144 hour visa free transit counter where you will fill out a blue form. Shortly after that, you will get a sticker in your passport and be allowed to exit the airport.