most unattractive looking BR diesels

[Sun Chariot]

The first few D6300s had them added some time after building, so they were a bit ungainly, but the later D6300s had them fitted from new and were better integrated into the cab front.

The things I learn. Five and a half decades on this soil and I've never noticed that subtle difference.
Those two pics on your post: now it's blimmin' obvious!
(I think I'll stick with BR era DMU stock...)

On a loosely-related point: I do wonder what the Ivatt twins 10000 + 10001 and the Bulleid trio 10201-10203 would've looked like with split headcode boxes. The Bulleids, I think, would have won the ugly award....

 

[Harpo]

The D8400s (class 16) are my ugly choice.

While the D8000s (20s) and D8200s (15s) turned out well, the 8400s managed to look as though no designer had touched them, complete with truly ugly grilles and ancient NBL spoked wheels. Even their ‘parent’ 10800 managed to look half decent. To be so poor operationally too was almost no surprise.