BK are offering a free item seemingly each day from 2/12/19 - 13/12/19 via their App. Please note that some of them are only valid on particular hours of the day. Confirmed so far:
2/12/19:Free chilli cheese bites between 2-4 PM
7/12/19: Free coffee between 9-11 AM
10/12/19: Bacon double cheeseburger for £1.99 all day
13/12/19: Free chicken fries between 2-4 PM
Check their app daily for each offer.
This should be national but unlikely to include service stations/airports etc. Will need to be confirmed.