@NeilParker-Qt Update
When contacting per email
Pearson VUE EMEA Customer Service PVEMEACUSTOMERSERVICE@PEARSON.COM
they will send you the voucher, but be sure to state clearly for which country it will be used, otherwise you get an error that the voucher is not valid in your country. After contacting them again I received the correct voucher which also worked fine. 50% off the full price.