Got the answer myself... Vouchers not transferable.
I tried to explain they're not being transfered if I'm the lead on the booking and travelling with my family but they were having none of it.
Seems a pretty crappy way to treat your customers who have taken vouchers as a leap faith rather than cash refund to be honest (Don't know why I'm surprised). I also contrast it with Legoland in Denmark who offered a voucher for the full cost of the stay, valid for a full 3 years, can be used in the shop, to book accommodation, to buy tickets as they just send a gift card to the value of the booking.