This is probably D6517 but we will never know for sure now! Note the DEMU a Class 206 (or 'Tadpole'). Formed in 1964 from a power car and trailer second from a short (58') 6-Car Hastings DEMU (class 201) plus a 60' driving trailer from a BR standard 2-EPB (the EPB motor coaches were then used with SR or BR trailers to form 4-car units). The Tadpoles were intended for the Reading-Guildford-Redhill-Tonbridge service, but it is possible this one was in Southampton to substitute for a failed Hampshire DEMU (for Southampton-Portsmouth, or less likely - Southampton-Alton via the Mid-Hants line).