According to the “Online Bike Museum” website, the marque, based in New Cross in south-east London, took the name from the nearby Marquis of Granby pub (this source dates its foundation to 1915 or slightly earlier), and operated until the 1960s. They used Granby in a wide range of adverts and brochures.
Since Granby Cycles got to the name first, it would be wonderful to know if they were Stephenson Blake’s inspiration for the name “Granby” or if this was a delightful in-joke. You can spot that it’s not Gill Sans from the straight leg of the 'R’ and asymmetrical '3'.
The Marquis (or Marquess) of Granby is a British aristocratic title given to members of the Manners family and named for a village in Nottinghamshire. The specific Marquis comemmorated is John Manners, who won a string of victories for Britain in the Seven Years War while taking considerable care by contemporary standards to keep his troops well-fed and treated, giving his name a traditional association with hospitality. The Dictionary of Pub Names reported that in 2006 at least twenty pubs existed named after him in London alone.