These class 166 are progressively being relocated to services that operate in and around Bristol, locally to Avonmouth/Severn Beach and Portsmouth - Cardiff services.
The class 166 are working Paddington Oxford services but with the electrification of the from Paddington to Oxford and South Wales. New electric class 387 EMU's will replace the 166 on the Oxford Service.
The class 166 is now some 25 years old and have been refurbished and updated. The class 150 and 158 will be refurbished and relocated to Devon and Cornwall.