He seems fine to me to be honest Caz. He's definitely on the bigger side, but nothing like a size that would concern me. The best way to tell is by looking at his back legs. If you could get a photo of them from behind and maybe with him on his back then that would be great. It's really hard when you have a lazy hoggie. Hercules was lazy. He was bigger than Oscar and he was healthy. He could ball up easily. If they are overweight then they can't ball.
What are you feeding him - both fresh and types of biccies? Also what do you feed him mealworm wise? Sometimes just a simple change can make a difference. I have to watch what I feed Belle because she's prone to putting weight on, bless her. She has a slightly different biscuit mix to the others. Barry is prone to being underweight because he doesn't eat much of anything - esp fresh he wont touch, so he has a higher fat biscuit mix. It's like a hoggie restaurant here - all needs catered for, haha! x x