Do I qualify for 72 hour free transit into China

Yes, your itinerary is eligible for 144 hour visa free transit, but under the following conditions:

- Your flight from, I assume UK, to Shanghai is not allowed to have any additional landing within mainland China and in the country where your cruise will have its first port of call, immediately after Shanghai
- Your cruise is not allowed to have its first port of call, immediately after Shanghai, in mainland China port

If the above conditions are fulfilled, you are definitely eligible for 144 hour visa free transit in Shanghai area. 72 hour visa free transit in Shanghai has been replaced by 144 hour visa free transit a couple of years ago.

Thanks for the info, perhaps I should mention our first port of call after Shanghai is Japan then we return to China stoping in Hong Kong on the 18th feb for 2 days, are we still ok for the 144 hour entry, we don’t return to China again on this trip

Yes, this is fine. Your itinerary or better to say a portion that is of interest to the Chinese authorities is:

UK - Shanghai - Japan

This is perfectly eligible for 144 hour visa free transit and you don't need any kind of visa. You should just print out your cruise ticket and you will present it both at check-in in UK and again in Shanghai upon your arrival at the airport at 144 hour visa free transit counter. After you have filled out a blue form at the mentioned counter, you will receive a sticker in your passport and be allowed to exit the airport.

Your port of call in Hong Kong is absolutely visa free because UK citizens don't need a visa to enter Hong Kong and Hong Kong by itself has separate immigration policy from mainland China.