The group has unveiled the offer, under an internal name Castle Premium, in the Spaniards Inn, Hampstead Heath, north-west London.
It was originally launched in The Engineer, Primrose Hill, also in north-west London, last spring and then the White Horse in Parsons Green, west London.
The company said the location of all three sites, affluent London “villages”, allowed it to upgrade the traditional Castle offer and that it would look at other opportunities to incorporate it in further pubs with similar demographics.
The offer includes food prepared fresh on the premises, speciality beers, real ales and ciders on tap, and beer and food-matching event