Can travelers from the United States purchase and use the British Rail Senior Pass?
Jan, yes, you can. You can even claim the discount before you have actually purchased the card, so if you buy tickets on line in advance of arriving in the UK you can choose the option that says you have a senior railcard. Then just buy the railcard when you get here and before you use any of those tickets. Just watch out for the times and other rules about when the card is valid: http://www.senior-railcard.co.uk/using-your-card/faqs/validity/