The Free Fruit Fridays will see McDonald's give out the equivalent of more than 3.5 million apples and 23 million grapes.
The offer is being promoted by a marketing campaign across TV, radio, press and digital. The TV adverts show parents and children enjoying finding fruit in places such as the garden, the countryside and also in McDonald's resaturants.
McDonald's UK director of marketing Nathalie Pomroy described the move as "a brand perception piece".
The chain has been selling the fruit bags for some time but sales have been in decline. Yet a similar promotion in France led to a 19 per cent rise in fruit bag sales outside of the promotional day.
Pomroy added: "It actually changed behaviour, and that's what we're hoping to replicate in the UK."