I'd go by train, but that is primarily because I think it is simply a more pleasent way to travel, and the price and time of transit are comparable. When I lived in Surrey, we took the train almost exclusively. But purchase ahead of time, if you can, to make things run smoother once you're there. It will just be once less thing to worry about.
Eat bangers. They're delicious, and can be found anywhere. Go sit in your local pub, drink a pint and listen to the locals while chomping on bangers (often served to be dipped in mustard, among other things, or with mashed potato). I missed them dearly (they're a comfort food to me) and was ecstatic when an Irish family opened up a pub near me that serves Excellent bangers and mash (I live in Wisconsin).
Congratulations! Enjoy yourself!
m