國鐵advance ticket問題 - 倫敦

我買了愛丁堡到倫敦的advance ticket
但現在事出突然，我當天得改去York

請問我可以中途下車嗎？需要收什麼額外費用嗎？
我沒有要求退差價（愛丁堡到約克的車票原本就比愛丁堡到倫敦便宜）
只希望能讓我下車出站就好。

因為看國鐵網站似乎不行，
但我不確定他的不行是「要求退差價」不行，
還是連「下車要出站（願意接受被罰款）」都不行
↑私以為這有點太強人所難，萬一車行途中家人發生什麼事要立刻跳車返回也不行嗎？
我覺得應該不會有這麼強硬的規定吧...所以才會好奇一問
http://help.thetrainline.com/app/answers/detail/a_id/3968/~/can-i-change-the-stations-im-travelling-between%3F

Q:Can I change the stations I'm travelling between?

A:(中略)

-Advance tickets

Advance tickets can offer great savings over the cost of buying a ticket on
the day of travel. However, they can only be used on the train you chose when
you booked, and you must get on and off the train at the stations specified.
While the date and time of Advance tickets can be changed, it is not possible
to change the stations you are travelling between.

--