In message , james007
writes
It's not an FAQ, and I've asked on the website, but do some of the
learned people here know the answer - I've a number of passenger
charter vouchers: how do I get these added to my pre-pay Oyster card?

Sorry for the delay in replying but I wanted to get the facts right.
AFAICS, you can use anything to top-up your Pre Pay at a ticket office
except Visitor Vouchers, Warrants (other than PERTIS) or Postal Orders.
--
Kat "A world without string is chaos"