MTV UK is doing a top 20 of Britney's best-selling singles and they called some guy from the official UK charts company to tell about her success on UK charts and he's talking about longevity and success of each and every one of them and, most importantly, telling the official sales for all of them.
I'm writing the sales down.
They began with "Amy" (105k) and now they are at "Born To Make You Happy" (325k).