Thanks to Stuart Davies we now know 5692 is the third loco in the line. These were the last two 56xx's working off Tondu.

A splendid image of Tondu Motive Power Depot from April , 1964 showing the squared roundhouse with its massive smoke ventilators on the corrugated asbestos clad roof installed in 1953 by the Western Region .
Tondu was known to have limited covered space for its allocation of locomotives and , as seen here , it was often necessary for a number to be left in the open when " On Shed "
The Depot was built by the G.W.R. in 1889 , replacing a much earlier and smaller 1865 built facility , and survived in service until February of 1964 .
This image reflects only too well the problems with colour photography at this time , with plenty of black grime and not much in the way of colour , apart from a faded buffer beam , some rusty smoke boxes and a few red bricks !