Hi Linda,
Greeting from Peggy, Top China Travel.
Whether you could have a visa free tour or not in Shanghai within 3 days depending on the following conditions:
1) Must have the departure air ticket from China to the third country, that means if you fly to Shanghai from UK, you need to hold a depature ticket to another country not UK.
2) The depature ticket must be booked beforeyou arrival airports in Shanghai and also the depature date must be within 3 days.
3) Hold a visa to the third country (third country is not China)
You can check about more details on
/shanghai/shanghai-72-hour-visa-free-policy.htm
Things must knows:
► You must have the confirmed airport leaving ticket before arrival, or you will be rejected to apply the visa-free right
► The 72-hours visa free time is valid since you finish the visa-free procedure but not the arriving time of your plane to above cities
► One visa-free permit only valid in one city, that means Beijing visa-free permit could ensure a visa-free policy in Beijing only, no applied in rest places in China
Peggy