Cheapest item it works with seems to be fries so burger and chips for £1.59.
Click & collect first order: Free whopper with purchase over £1
A free whopper with your first purchase using click &
Collect with a minimum spend of £1. Participating restaurants only.
How to redeem:
1) sign in, click 'add to mobile order' & select restaurant
2) add whopper or plant-based whopper to basket
3) add one or more products so basket total is over £1