SWT have both Class 159's and some 158's
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The plan though would be for them all to get it- and the reformed 460s. As there wouldn't be any "old spec" 458s at the end, it's up to the magical elves that make TOPS decisions whether to give them a different sub class number, give them a new class number or do nothing
The official plan is that:
458.001 - 458.008 remain as 4-car units
458.009 - 458.030 become 5-car 458.509 - 458.530
6 new units from Class 460's will be 458.531 - 458.536
(This uses 52 of the 64 class 460 cars)
The 8 Class 460 luggage vans would be scrapped, 2 driving motor cars and 2 intermediate toileted trailers kept as spares.
No Gatwick cabs are kept, all 12 new cabs will be Class 458 types, though ALL CLass 458s would be made mechanically coupling compatible with Class 450s.
In appearance then all vehicles will be in SWT livery but ex-Cl.460 vehicles will PROBABLY retain the ribbon effect glazing and side-skirts and so aid their identification!
Rumour is that if the DfT authorise anything soon, it will be this conversion as it is best value for money...