I'm planning to travel tomorrow from Whitechapel to Oxford and when making sure that the ticket machines at Whitechapel will sell me that itinerary (wasn't sure since it's an underground station) I noticed something strange. Online an off-peak return from Whitechapel to Oxford with a railcard is £23.20, but from the ticket machines the same ticket was £24 (plus some amount of pence which I've forgotten). Any idea why this is and is it possible to get the machine to sell me the cheaper ticket? (Unfortunately I can't buy online and collect as Whitechapel doesn't allow collection of pre-booked tickets). £23.20 is the fare advertised on nationalrail.co.uk, so it's not split tickets or anything like that.