Not content with the accolades the client has picked up over the years, it has approached the Guinness Book of Records.
The ad, written by a Guardian journalist and adapted by the agency, boasts 3,757 words and, unsurprisingly, looks to appeal to people who like to read.
You'd have to be a pretty devoted reader to get through the entire thing, which roams around the subjects of Ivy Compton Burnett and the joys of children's literature (Harry Potter had to get in there somewhere) only popping the Guardian reference in at word number 3,738.
Amazingly, as well as running in its full glory in the newspaper, the ad has run at a mere 2,264 words as an outdoor campaign on the London Underground.
"There's kind of an inbuilt test," Andrew Fraser, the creative director on The Guardian, says. "If you are the kind of person to read the Review section, you'll read the whole ad and, if not, then you'll skip to the end where you'll find the Guardian message."
Surely more a test of how many Tube trains you're prepared to miss to make it to the end.