For convenience on my return from trips abroad I often buy tickets to and from Heathrow Underground (starting from Rainham Kent) in advance over the internet and collect them from the machine at Rainham on my way to the airport. If I buy these as two singles - for example one peak and the other off peak with a network card - then the tickets from Heathrow never work the gates on the Underground. Fortunately I have not had any problem in getting the LUL staff to let me through.
What am I doing wrong?
What am I doing wrong?