They used 158s up until the early the early 2000s on things like Manchester Airport to Edinburgh, Portsmouth to Blackpool, Gloucester to Swindon (for some reason originally a XC route, which had contracted operation to Wales and West). They all ended up going to Arriva Trains Northern, where they then were divided between Transpennine Express and Wessex Trains. They've finally all gone the way of First Great Western I believe.
They had a slightly different, and some might say more comfortable interior, and carried an Intercity badge on the front panel on the left hand side above the light clusters.
The 158s are still with FGW. They used to run on Virgin's former VT0 route from Swindon to Birmingham New Street, calling at Kemble, Stroud, Stonehouse, Gloucester, Cheltenham Spa, Worcester Shrub Hill and Birmingham New Street.