Re Loco 3591, what my books tell me is this. It did not pass into BR ownership in 1948, although a few of this class did but all were withdrawn in 1948/9.
The loco was built September 1899, and its first shed was Paddington (sic); i.e. not Old Oak Common.
Its last shed was Swindon, and it was withdrawn from there in May 1936.
I agree that the rails are so close together that it cannot be St. Blazey where they pass through arches. They are going to a turntable just out of the picture, which means a roundhouse. I do not recognise it as Laira, which did have a roundhouse. A few sheds which also had roundhouses:- Old Oak, Bristol SPM, Swindon, Taunton, Wolverhampton (Stafford Road and Oxley), Tyseley, Stourbridge junction, Shrewsbury, Croes Newydd, Ebbw Junction, Cardiff Canton, Tondu, Pontypool Road, Aberdare, Neath and Llanelly.
My guess would be Swindon, but cannot be sure without a list of all the sheds it was allocated to.
Regards Mike Many thanks for all of this information but can anybody pin down this location precisely please. This superb image was provided by Micheal Morant from his expensive collection, it was first recorded as being at Truro and then later moved to suggested location at St Blazey. However this is now incorrect.