Colchester Corporation 42, OVX142D, a Leyland PD2A/30 with Massey H33/28R body, new in 1966.
The batch of six were fitted with platform doors in 1970 - it looks from the photo that the doors had been fitted. Withdrawn in 1979.

Photo taken by Ian Banks, early 1970s, Entering Colchester Bus Station
Click here for Ian's Fotopic site