to add a little trivia: this one has the fastback seat stay treatment known as "Brampton-Victor" or sometimes shortened to just "Victor".
It's been disputed, but Bob Freeman (Elliot Bay Cycles in Seattle) gathered some definitive info that Geoffrey Butler was brother of (the more famous) Claud Butler of London-Clapham (later acquired by Holdsworth/Holdsworthy). Guess they were not only competitors in the bicycle business but didn't admit their relationship to the public...may have been some bad blood there.
The other famous builder in Croydon was Chas Roberts, does anybody know if Roberts ever build for G. Butler?