I forgot to say - the answer was
"Congratulations youve found and completed the REAL challenge. Your win code is <obscured>.
Please email this code to our team at <obscured>. If youre the first person to do so, and can prove you meet the eligibility criteria (British citizen currently resident in the UK) we will be in touch to advise how to claim your prize. Well done and good luck in the Cyber Security Challenge competitions taking place throughout the rest of the year."