(31 Dec 2013, 8:24 pm)Dan wrote I think the only problem that would arise from that is the 2A/2C operation.
There are some journeys which are presently numbered 'M2A', which would presumably take the form of the '2A' in your suggestion.
Oh dear... forgot about that! Maybe it's not such a good idea, as it would involve re-numbering the 2A/2C and 'South Tyne 5'.
Maybe renumbering the M2/M2A and M3 as the W1/W1A and W2, and then W5 and W6 as W3 and W4 would work, although it's probably not worth it. It just seems odd having the M2 and M3, but no M1 any more.