Peter Kerslake says "This is the western end of Basingstoke station and 6849 "Walton Grange", complete with Western Region lamps is most probably on a through working from the Midlands running via Banbury and Oxford down to the South coast, a service which until the end of the 1962 Summer Services would have taken the Somerset and Dorset line across the Mendips before those services were curtailed by the Western Region that year.
6849 had been a Cornish engine based at Truro a few years earlier, and this view shows Basingstoke station before the third electrification work had begun the following year.
I wonder how far into Southern territory the engine will work?"

This looks to me like the Newcastle-Bournemouth, going by the green Mark 1s and the angle of the shadows.