Originally Posted by DeathSlam

When I booked my outbound I was told on the phone that they can add the return on the vouchers if you ring up (same as Amex vouchers). I will find out on Saturday when I try it.
But when you make the initial outbound booking you will have to make sure they use *both* vouchers, otherwise they will use up one whole voucher (easier for them) and then the return will be on a separate ticket.
Although to be fair, depending on your point of view, having the two bookings separate could actually be an advantage.