Avon with an aft fan

From Bill Gunston’s ‘The Development of Jet and Turbine Aero Engines’

By 1960 it looked as if the suddenly created JT3D was going to take the rest of the ‘big jet’ market, but Rolls still had good business with the smaller Comet and Caravelle. Quickly an aft fan was designed and fitted behind an airline-style Avon achieving a world-record low sfc, but it got nowhere.

Does anyone know what engine this was and why it didn’t get anywhere?