Are you sure about that? SWT (Stagecoach) ordered its 450s in April 2001, after its own less-than-successful procurement of 458s (the DC version of the 334) . Both the 360s and the 450s entered service in 2003 = I recall tghe 450s were delayed because a power upgrade was needed (lack of co-ordination between SWT, Siemens and Railtrack)
Not so. First Group took over the GW and NW franchises in Feb 1996 and March 1997 respectively. The 175s were ordered in July 1997 and the 180s in October 1997
Strictly, the BR MBO Great Western Holdings (which had a FirstGroup share) took over the North Western franchise (NWT) in March 1997, and were bought out by FG in March 1998 to become FNW.
I don't think NWT actually placed Coradia orders before FG took over, but had selected the Alstom design.
NWT had plans to run a mix of 175s and 180s, with the 180s running into Euston from North West/North Wales origins.
They abandoned the idea of running to Euston when they discovered their finances were in trouble, and the Coradia order was placed by FG as 27x175s for FNW and 15x180s for FGW.
175s have been maintained at Chester by Alstom throughout, while 180s were maintained at Old Oak by FGW themselves.
180s have never really had a "home", and the 175s are about to be evicted from Chester by the CAF 397 fleet, CAF now owning the depot.
175s are also reported to have corrosion issues, and 180s are likely to be the same, so the long-term future of both fleets is in doubt.
The origin of the Desiro UK fleet was in the class 332s for Heathrow Express (1997), which were built by CAF but had a Siemens traction package.
Once Stagecoach fell out with Alstom with the class 458s, Siemens had an easy route for the SWT class 450 order, already having acceptance on the electrics.
In the event too many 450s were ordered for SWT, so the last tranche was reengineered and diverted to WCML suburban services as class 350s.