The actor - who portrays Harry's chubby cousin Dudley in the movie - lost so much weight prior to filming on the movie he had to don facial and body prosthetics for continuation purposes, something he found "amazing".
He said: "I do look a bit different because Dudley was a very piggish character and about 3 years ago I lost quite a considerable amount of weight.
"It was quite funny because I had a big fat suit on in this film and face prosthetic. It was bizarre, you feel really big and my mobility was affected. However it is amazing to feel light but within someone that should feel really heavy, so that was a fascinating contrast."
Despite appearing in 'Harry Potter' and BBC One TV series 'Merlin', his future hope is to appear in theatre.
He said: "I am auditioning again, getting back to theatre would be amazing. I have had a really lovely year this year so it would be nice to repeat that."
When you're the chosen one, like the boy wizard Harry Potter, expectations surrounding your arrival...