Presented at the London Motor Show in 76 and again at the 77th Geneva Motor Show, Ten Twenty was a concept developed by the Triplex car glass company based on the Alfasud mechanics and designed by Chris Humberstone, characterized by its 6 seats and roof in removable glass.

The Triplex Ten Twenty Special, name often shortened to Triplex TTS, was subsequently renamed to be called the Sextet. I do not know if the Triplex name was dropped and the car was to be placed under the Hunberstone Design umbrella. It did appear in a Humberstone Design brochure.