I don't know if he's purposely picking up and dropping an accent, but I agree that it changes quite a bit, even when he's talking to the camera. I think it comes on more strongly when he's feeling smug, like it's a cocky persona he uses to help him think like a winner. Last week, he said "legless chickens" and "sleek weasels" in a Bond-villain way, but in yesterday's episode, when he said he might be "high and dry" now that Jacquie's gone, he sounded genuinely dejected and had no trace of an accent.
Zhillbear
Channel Guide Magazine