Complex sentence: The Class 800 trains will come into service on the Great Western Main Line from 16 October 2017 on a service to/from Didcot Parkway and London Paddington, as well as on the East Coast Main Line from December 2018.
Split into simpler sentences: The Class 800 trains will come into service on the Great Western Main Line from the 16th October 2017 on a service to/from Didcot Parkway and London Paddington. As well as on the East Coast Main Line from December 2018.