We will be traveling to different areas in England by train and plan to buy a National Rail pass. I understand this pass would qualify us to use the 2FOR1 vouchers for attractions in London. We will be arriving by train in London from Liverpool on a Sunday then traveling to Heathrow by the express train on Wednesday. Could someone explain how to claim and use the vouchers? Thank you for any guidance.
Don’t know about the vouchers but the Elizabeth Line is virtually always a better option than the HEX, as is the Piccadilly (tube) line, to Heathrow.
What kind of National Rail Pass are you thinking of? If you mean a BritRail Pass, it is accepted for 2-4-1 tickets only at certain venues; apparently they say so on their website.
You can read all the specific rules here. Note that the Heathrow Express does not qualify for 2-4-1 tickets.
https://www.nationalrail.co.uk/days-out-guide/train-fares-discounts-and-ticket-validity/