A tongue-in-cheek whistlestop tour of the life of a Walkers crisp will be told in a new TV ad designed to flag up how it is made from British potatoes, Sunseed oil and seasonings free from artificial colours or preservatives. The ad which will air from 12 September shows a potato being plucked from the ground before it is chipped, seasoned and eaten by Gary Lineker, who appears only at the end of the advert.