According to a article in todays western mail the Great western mainline is only being electrified as far as Bristol with dual fuel trains being used on the services to south wales according to a senior member of Network rail.
I can say the WAG is already up in arms about this.
Sounds like someone misinterpreted the plans, which most likely call for a temporary halt at Bristol, then continue to Wales. BR's original plans for electrifying the ECML in the sixties called for wires to Newcastle but no further, but they realised this was a bit silly later on. Presumably, it's one or the other.