Due to the quantity of Class 25s constructed they were originally numbered in two completely separate D series number ranges. Carrying on from the Class 24s, from which they had developed from, D5151 upwards to D5299 then from D7500 onwards as the number range from D5300 onwards had already been taken.
As with the Class 24s the 25s, as these were designated under the TOPS renumbering scheme, there were several Sub Classes and again, like the 24s, during the renumbering to TOPS no distinction was implemented.

25/0: D5151 – D5175 (25001 – 25025)
25/1: D5176 – D5232 (25026 – 25082)
25/2: D5233 – D5299, D7500 – D7597 (25083 – 25247)
25/3: D7598 – D7677 (25248 – 25327)

Designated as Class 26 there were two Sub classes but as with the 24s and 25s the renumbering scheme did not make any distinction between these when implemented.

26/0: D5300 – D5319 (26001 – 26020)
26/1: D5320 – D5346 (26021 – 26046)

Designated as Class 27 on renumbering from the D series to TOPS series those Class 27s that remained in standard form were renumbered into the 27/0 Sub Class whilst those already modified to work the Edinburgh / Glasgow push pull service were numbered into the 27/1 Sub Class. No allowance was made for early withdrawal D5383.
Later modifications to several members of the 27/1 series saw a batch of locomotives being reclassified as 27/2 subsequently being renumbered from the 27/1 271XX series into the 27/2 272XX number range. To complicate matters 27118 was again renumbered within the 27/1 series to 27103 to fill a gap left by original 27103 which had been reclassified to 27/2 resulting in the number 27103 being used twice.

Initial number ranges on renumbering to TOPS...

27/0: 27001 – 27044
27/1: 27101 – 27124

Number ranges after creation of the 27/2 Sub Class…

27/0: 27001 – 27044
27/1: 27101 – 27112 (27118 becoming the second 27103 replacing the original 27103)
27/2: 27201 – 27212 (27103, 27113 to 27117, 27119 to 27124 becoming 27/2s but not in sequence)

After displacement from the Edinburgh / Glasgow push pull service by Class 47/7s the surviving 27/1 and 27/2 series locomotives were renumbered into the 27/0 series from 27045 onwards. Whilst all the 27/1 series locomotives underwent renumbering to the 27/0 series half the 27/2 fleet; 27201, 27202, 27203, 27206, 27207 and 27208 had all been withdrawn by this time and the numbers 27057 (for 27203), 27060 (for 27206), 27061 (for 27207) and 27062 (for 27208) remained unused. No numbers in the 27/0 series were allocated for 27201 or 27202 as both these had been withdrawn some time earlier.

Final number range…

This fleet of locomotives were originally classified as Class 30 but prior to renumbering from D series to the TOPS number series the whole Class had been re-engined and reclassified to Class 31. The build was numbered in the ranges D5500 to D5699 and D5800 to D5862 as the series D5700 onwards had already been taken.

On renumbering into the TOPS series the Class was split into three Sub classes.

31/0: D5500 – D5519, prototype locomotives with different control equipment from the standard build.
31/1: D5520 – D5699, D5800 – D5862, standard build locomotives.
31/4: Random numbers, standard build locomotives fitted with ETH.

One anomaly to mention at this point is that D5518, one from the prototype batch, had by the time of renumbering been rebuilt to the same spec as the standard build locomotives so it became 31101 at the start of this series., the rest of the prototype batch being renumbered in the 310XX number range. The standard build locomotives were renumbered into the 311XX, 312XX and 313XX number ranges whilst the locomotives already fitted with ETH were renumbered into the 314XX series. As the program to fit ETH to several members of the Class was underway at the time of renumbering two locomotives that had been allocated a 31/1 series number were out-shopped from works numbered in the 31/4 series, their allocated numbers 31104 and 31267 remaining unused.

D5522 was allocated to become 31104 but became 31418
D5697 was allocated to become 31267 but became 31419