LMS Stanier 2 Cylinder 4MT 2-6-4T no. 42566 near Bradwell on September 29th, 1962. Following on from a viewer's query concerning the coaching stock I've received extensive facts and thoughts from David Woodcock:
"I had noticed that it was an emu but hadn't realised the significance of the shot. Firstly, the emu is an Eastern Region AM7 unit which had been built originally at Eastleigh c1956 for 1500v DC outer-suburban work ex-Liverpool Street to Southend, Clacton and Walton; as built they had driving trailers at each end. When these lines were converted to AC (initially 6.25/25kV), Eastleigh rebuilt the units to suit and in the process the brake van was moved from one of the middle cars to one of the end ones - which one can see in this photo.
The set not only has a half-yellow front end but is LINED, so it wasn't just buffed at Wolverton, it was REPAINTED there. Now the sets had been rebuilt at Eastleigh between 1960 and 1962 and such was the scale of the rebuild that they must have been fully repainted then even though the SR repaint ethos of the time was "revarnish at 3-years, repaint at 6". So here we have this unit being specially repainted.
I have never seen a photo of another ER set lined, other than the Clacton Express units which, almost uniquely, were lined maroon."
My own tuppence worth is that, although I had identified the stock as an EMU, I hadn't any idea that it was an ER overhead set but my first thought, regardless of which type of unit it was, was that this was a one-off paint job undertaken at Wolverton and possibly to exhibition finish but which exhibition is the question?