Originally Posted by
enviroian
So there is a kiosk at the Lhr underground where I can pick it up?
Not in the Underground station but from the rail ticket machines in the terminal. According to the trainline.com these are:
T2 and 3 - Opposite the Heathrow Express Ticket desk in the Central Terminal area - this is after you enter the station and before the lifts to platform level. [Note this is different to the Underground station - you walk past the rail station if going to the Underground from T3, but not from T2. I believe there are also machines in T2 and T3 Arrivals itself but am not 100% certain of this.]
T4 - on the Arrivals level opposite the Heathrow Express Ticket desk.
T5 - to the left of the ticket desk on Arrivals level.
Another frustrating thing is the ticket doesn't say what platform. I do know it's usually 5 or 6 (the escalators in front of the Starbucks and that sushi place) but from there I have to flag down an employee to find out what platform the next express/fast train to Ashford International is. Ugh.
You can find out live platforms for any train from the National Rail website or app, or that of any train operating company. However the Southeastern platforms at St Pancras are always 11-13.