What a lovely picture.
The train is of very uniform appearance for the LNWR and I believe all the carriages are either 30ft 1in or the contemporary 42ft stock:
D385 30ft 1in Brake Van
D297 30ft 1in 5cpt Third (2 off)
D165 42ft lavatory luggage compo
2 further 42ft lavatory carriages
I'm not sure whether the last vehicle has six or eight wheels, but it appears to have an ogee in the centre.
As one would expect, there are lavatories for the First class passengers only. In my opinion the train is unusual because often when there are two Thirds and a van at the front they have been added to a standard set, and that set usually has a Brake-end at either end of the train. The LNWR liked brake-ends and had very many of them, but not on this train.
As for a date, the lack of lower footboards means post-1901 and the single whistle on the engine means post-1903. The fine and high ballast suggests perhaps pre-War, but I can't get any nearer than that. | 
