One mystery cleared up - thanks
And after they were stopped being used in January 1976, certain classes that were about to be withdrawn anyway used them to display their old pre - tops numbers, some of which they still carried, like the 'Westerns'.
Here is
D1028... 1028 Western Hussar, outside Paddington in 1976:
With D1051, Western Ambassador:
D1028 was the second last Western to be scrapped in 1979, but, here it is with D1023 Western Fussilier, which is now preserved at the National Railway Museum at York:
It was the only one of it's type to get a 'domino' type headcode box instead of just displaying the number, and was also the last of it's type to run in February 1977 along with D1013 Western Ranger and one or two others (D1010 Western Campaigner, D1048 Western Lady, etc).
They were BR's last ever Diesel Hydraulic locos: