Please, please , please don't even consider using the dreaded Trainline.com. They can never offer any fares lower than you'll find by going to
http://www.nationalrail.co.uk/
Further, they might add a booking fee or (even worse) supply you with tickets that aren't even valid for travel on any train. (I used to run a railway station and I got fed up of explaining to people that their tickets weren't valid, meaning that they'd have to pay again if they wanted to travel, and then try to get a refund from Trainline.com ).