Walker's was the original British brand which was then acquired by Frito-Lays 50 years after the Walker's brand was established so they kept the name the same for Brits and used the new name Lays for the rest of the world.
The factory in Leicester is the biggest crisp production plant in the world and produces 11 million packets of crisps a day. (Guess which Wikipedia page I'm reading en)
I give out Lays to people when I forget about their clitoral hoods.