Definitely the oddity in Southend's fleet of 23 Routemasters was 121, CUV256C, the former RCL2256. Southend's only 30 foot example, it had started life as a Routemaster coach with London Transport in 1965. Towards the end of its life in London it was demoted to bus work on route 149 with its platform doors removed. It went on to become unique after a rear-end accident, when its rear was rebuilt to standard Routemaster open platform style.
Here in Southend service it is at the Landwick terminus of service 4 from Southend via Wakering. The Thamesway Mercedes minibus behind reminds us that this was the era of the bitter bus war between the two operators, which took Southend's bus fleet to an all-time record size of 115 buses (plus 17 coaches) in June 1992 but which also virtually bankrupted the company and led to its sale to British Bus.

Photo from the Peter Cackett collection, photographer unknown, taken Landwick terminus