That was the situation in 1997 but it doesn't follow that a new government couldn't have put more money into BR (if it had still existed) and decided to electrify the sidings etc before a rolling programme
But history demonstrates there was no money or interest - otherwise we wouldn’t be in the situation we are now.
BR had zero interest in electrifying the Great Western. BR(W) signalling as installed in the 60s and 70s was incompatible with electric traction; and was NOT life expired in the 1990s. Heathrow Airport paid for the necessary resignalling to enable electrification for the bits of railway they intended to run on - which saw the closure of Old Oak PSB and its replacement with Slough New IECC. With a further 20 years expected life out of existing assets not compatible with electrification; stagnant at best passenger numbers along the M4 corridor; and a poor business case for Crossrail Mk1 resulting in its shelving – BR/NSE went with Diesel units for fleet modernisation in the early 90s - it’s not as if with the rest of the Networker project there wasn’t already an AC design on the drawing board / production line of BR/NSE has wanted it.
Heathrow Electrification wasn’t an isolated scheme in the context of BR as a whole - it followed the successful wiring of the Birmingham Cross-City route, the ECML north of Hitchin, Leeds/Bradford/Ilkley and the BedPan line. You could argue it was scandalous that electrification didn’t continue beyond there; but with the exception of Heathrow all those schemes were to phase out life-expired assets. What was left beyond that was either infeasible or wasteful obsolescence of new or nearly new rolling stock and line side equipment.
With privatisation around the corner the last thing the government wanted to be doing was committing more massive capital expenditure upgrading infrastructure they were about to sell off at a knock-down price to Railtrack.
Plus, 1990s Electrification is generally the nasty headspan Mk3 equipment which falls down all the time (at least when installed on BR’s budget). I’m not sure we want a second East Coast Main Line...
GW Electrification (so far) has come at the right time. The signalling assets were reaching their 50 year lifespan from the mid-2010s onwards; similarly the high speed / long distance rolling stock was hitting the end of the bathtub curve for reliability. The requirement to replace both offered a sensible opportunity to wire the line.
A gentle, rolling electrification programme is good for the industry – the current indeterminate hiatus is not.