Looking into this with the help of my assistant, Claude, it seems that the fonts actually varied very slightly according to the class of locomotive, as they were cast in the foundries of each of the individual manufacturers. This suggests that classes 82 and 84 would have shared the same font, but the other 3 of the original classes might have all varied very slightly. AL6, being both EE made (class 83) and BR Donny made (class 85), might have had different fonts according to where they were made, that would have been the same as on the classes in the brackets above.
The plot thickens ......!
The AL2/Class 82s were built by Beyer Peacock in Manchester. The AL4/Class 84s were built by North British in Glasgow, so they were not cast in the same foundries.
The cast numbers can be grouped by the material and how they were fixed to the locos:
AL1/Class 81 (E3001-E3023 and E3096-E3097), built by AEI/BRCW - Stainless steel, screwed to the cab side from the front via countersunk screws.
AL2/Class 82 (E3046-E3055), built by Metro-Vickers/Beyer Peackock - Aluminium, screwed to the cab side from the rear.
AL3/Class 83 (E3024-E3035 and E3098-E3100), built by EE Vulcan works - Stainless steel, welded to a plate that was then screwed to the cab side.
AL4/Class 84 (E3036-E3045), built by GEC/North British - Aluminium, screwed from the rear to a plate that was then screwed to the cab side.
AL5/Class 85 (E3056-E3059), built by AEI/BR Doncaster - Aluminium, screwed to the cab side from the rear
AL6/Class 86 (E3101-E3200), built by BR Doncaster & EE Vulcan works - Aluminium, screwed to the cab side from the rear.
Two classes used stainless steel numbers that differed in their mounting methods, though they were probably cast from the same patterns and mounted differently (AL1 drilled through and countersunk, AL3 undrilled and welded to a plate). The other 4 classes used cast aluminium numbers with the same mounting method (though on the AL4s they were mounted onto a plate first rather than directly onto the cab side).
This Facebook post has a picture showing 5 complete plate-mounted examples - EE AL3s E3024, E3035 and E3099 (stainless) and NBL AL4s E3037 & E3045 (aluminium). There is also a further picture of a stainless steel '1' from an BRCW AL1 (with the countersunk holes for front mounting).
This auction lot shows the screw-on stainless numbers from BRCW AL1 E3003.
This auction lot shows the screw-on stainless numbers from BRCW AL1 E3010 (though the listing describes them as aluminium).
This auction lot shows the screw-on stainless numbers and double arrow from BRCW AL1 E3019.
This auction lot shows the aluminium numbers from Beyer Peacock AL2 E3046.
This auction lot shows the aluminium numbers from Beyer Peacock AL2 E3048, including a rear view showing how they were screwed on from the rear, with the screws in the same positions as the holes in the AL1 stainless numbers.
The auction lot for EE AL3 E3024's plate from the FB post above. There is also a rear view that shows they were welded on (no visible screws).
This auction lot shows the plate and stainless numbers from EE AL3 E3025.
This auction lot shows the plate and stainless numbers from EE AL3 E3029.
This auction lot shows the plate and stainless numbers from EE AL3 E3030.
This auction lot shows the plate and stainless numbers from EE AL3 E3031.
This auction lot shows the plate and stainless numbers from EE AL3 E3032.
This auction lot shows the plate and stainless numbers from EE AL3 E3033.
This auction lot shows the plate and stainless numbers from EE AL3 E3034.
This auction lot shows the plate and stainless numbers from EE AL3 E3303 (later renumbered E3098).
This auction lot shows the plate and aluminium numbers for NBL AL4 E3036. There is also a rear view showing the mounting screws, which are in the same positions as those for AL2 E3048 and the holes on the AL1 stainless numbers.
This auction lot shows the plate and aluminium numbers for NBL AL4 E3038.
This auction lot shows the plate and aluminium numbers for NBL AL4 E3040.
This auction lot shows the aluminium numbers for BR Doncaster AL5 E3084.
This auction lot shows the aluminium numbers from BR-built AL6 E3103.
The
auction lot linked to earlier shows the aluminium numbers from BR-built AL6 E3136.
This auction lot shows the aluminium numbers from EE-built AL6 E3160.
This auction lot shows the aluminium numbers from EE-built AL6 E3173.
This auction lot shows the alloy 'E3' and double arrow from an AL6.
Comparing all of those examples, I'm pretty confident that all the numbers were cast using the same patterns. The screw mounting positions for the stainless and aluminium numbers (across different locomotive manufacturers) being in the same place is pretty telling.
As for the typeface, I suspect it is a composite - I have looked through my period typeface reference books and cannot find a match that had all of the numbers in the same face. The style of the '1' in particular is not really found alongside a diagonal '3' (the chiselled-off diagonal of the '3' is quite unusual as well). At a guess, I'd say the '3', '6' and '9' (the latter two appear to be the same numeral, just inverted) come from a different typeface from the rest of the numbers.