I think I got into trouble today for not taping in and out from finsbury park and taking the Piccadilly line and then the metropolitan line to my University. Thankfully there weren't any ticket inspectors so I didn't get a penalty or fine, but I'm pretty sure I got charged the maximum fare...
My question is, is that if I took the great northern train to kings cross from hatfield railway to finsbury, where do i tap in and out before changing to piccadaly?