The claim we all swallow 5.5 grams of microplastic each week – the same as the weight of a credit card – has been repeated by charities, newspapers and the World Economic Forum.

But when you understand how this number was calculated, and the range of possible answers for the amount of plastic you eat, you might not want to repeat it yourself.

Professor Jamie Woodward from the University of Manchester explains what’s what.

Presenter: Kate Lamble