What did you buy in Pret? The 5% rate applies to hot takeaway food and hot takeaway non-alcoholic beverages.
If you sat/dined-in, it would also apply.
Hospitality
If you supply food and non-alcoholic beverages for consumption on your premises, for example, a restaurant, café or pub, you’re currently required to charge VAT at the standard rate of 20%. However, when you make these supplies between 15 July 2020 and 12 January 2021 you will only need to charge 5%.
You will also be able to charge the reduced rate of VAT on your supplies of hot takeaway food and hot takeaway non-alcoholic drinks.
Taken from Gov.uk