The Class 350/1 units were originally part of an order for 32 five-car Class 450 units for South West Trains.
However, they were never built as such.
Of the 160 carriages ordered, 40 were diverted as an additional 10 four-car Class 450 units, and the remaining 120 were modified as 30 four-car Class 350/1 units.
 The top speed of the fleet was originally 100 mph (160 km/h), but all 350/1s were modified to allow 110 mph (180 km/h) running from December 2012, in order to make better use of paths on the busy West Coast Main Line.

A second batch of Class 350/2 units, intended to replace the Class 321 units, was delivered in late 2008 and during 2009.
The first of the Class 350/2 was launched on 8 October 2008, and carried invited guests around the Wildenrath Test Track.

The last of the Class 350/2 fleet (350 267) was officially delivered to London Midland on 30 July 2009.
Class 350/2 differ from the Class 350/1 units in two key aspects: they have 3+2 seating in standard class (because they work short-hop commuter services, the Class 350/1 are 2+2 throughout, work longer distance services) and lack the dual-voltage capability of the 350/1.
Initially, Class 350/2 units had a maximum speed of 100 mph (160 km/h), but the fleet was upgraded to allow 110 mph running during 2012.
This was to allow the operators to run mixed 350/1 and 350/2 services without causing delays, especially important given the capacity changes which HS2 works at London Euston were expected to cause.

Class 350 trains are nearly identical to those of Class 450.
The latter class is only fitted with traction equipment for Southern Region 750 V DC third rail, whilst the Class 350/1 units can operate from either  25 kV 50 Hz AC OLE, as is done in regular service, or alternatively third rail.
 This dual-voltage capability was utilised when several units were leased to Southern in 2008 and 2009, in order to cover for similarly equipped Class 377/2 units temporarily sub-leased to First Capital Connect, themselves to cover for delays in the construction of the 377/5 fleet.
 All Class 350 units built since are not equipped for third-rail use but, like most modern British EMUs, can be retrofitted if necessary.

Every set of doors has its own set of guard-operated door controls behind a lockable panel.
The cabs have three radio systems - Cab Secure Radio (CSR), National Radio Network (NRN) and the newest system, GSM-R. CCTV and dot-matrix destination screens are fitted throughout the train.
The Class 350/1 units were originally part of an order for 32 five-car Class 450 units for South West Trains. However, they were never built as such. Of the 160 carriages ordered, 40 were diverted as an additional 10 four-car Class 450 units, and the remaining 120 were modified as 30 four-car Class 350/1 units.  The top speed of the fleet was originally 100 mph (160 km/h), but all 350/1s were modified to allow 110 mph (180 km/h) running from December 2012, in order to make better use of paths on the busy West Coast Main Line.
A second batch of Class 350/2 units, intended to replace the Class 321 units, was delivered in late 2008 and during 2009. The first of the Class 350/2 was launched on 8 October 2008, and carried invited guests around the Wildenrath Test Track.
The last of the Class 350/2 fleet (350 267) was officially delivered to London Midland on 30 July 2009. Class 350/2 differ from the Class 350/1 units in two key aspects: they have 3+2 seating in standard class (because they work short-hop commuter services, the Class 350/1 are 2+2 throughout, work longer distance services) and lack the dual-voltage capability of the 350/1. Initially, Class 350/2 units had a maximum speed of 100 mph (160 km/h), but the fleet was upgraded to allow 110 mph running during 2012. This was to allow the operators to run mixed 350/1 and 350/2 services without causing delays, especially important given the capacity changes which HS2 works at London Euston were expected to cause.
Class 350 trains are nearly identical to those of Class 450. The latter class is only fitted with traction equipment for Southern Region 750 V DC third rail, whilst the Class 350/1 units can operate from either  25 kV 50 Hz AC OLE, as is done in regular service, or alternatively third rail.  This dual-voltage capability was utilised when several units were leased to Southern in 2008 and 2009, in order to cover for similarly equipped Class 377/2 units temporarily sub-leased to First Capital Connect, themselves to cover for delays in the construction of the 377/5 fleet.  All Class 350 units built since are not equipped for third-rail use but, like most modern British EMUs, can be retrofitted if necessary.
Every set of doors has its own set of guard-operated door controls behind a lockable panel. The cabs have three radio systems - Cab Secure Radio (CSR), National Radio Network (NRN) and the newest system, GSM-R. CCTV and dot-matrix destination screens are fitted throughout the train.
British Rail Class 350