Southend 263, GLX913, was withdrawn in June 1962 and transferred to the Southend on Sea County Borough Constabulary, fitted with platform doors and converted as a mobile road safety exhibition unit (visiting schools, etc). Passed to Essex Police in April 1969 and sold in 1974 for preservation.
Initially restored back in SCT livery as 263, it has recently appeared in the Police livery, albeit still fitted out internally as when a bus rather than as the training unit. It has also appeared in a pseudo Derby Corporation livery whilst in preservation.
Click here for fleet details.

Photo taken by Richard Delahoy, Sunday 10 October 1999, Canvey Ralley