Will 2 of 1 vouchers be honored for travelcard purchased from non National Rail Stations, e.g. Tube or other outlets.
The 2for1 offers are sponsored by National Rail so you must go to a National Rail station and buy a paper travelcard with the National Rail logo on it.
No, they will not honor that. It must have the national rail logo on it. and Both people must have travelcard issued by National Rail.
Paddington station has a National Rail counter (First Great Western) and they have the daysoutguide brochures if you didn't print out your coupons in advance (though only 3 to fill out in each brochure)
I know there are others that do, but if you come from Heathrow to Paddington that makes it easy.