I'm fairly certain it's DMS. Having said that I could be wrong. What makes me almost certain (besides the taste and smell, along with the hit of sulphur I got from opening the lid for the first time) is that because of my set up I break almost every preventative rule in the book; I boil on a glass top electric stove, so the only way to maintain anything near a rolling boil is to partially cover the lid for a large percentage of the boil. I also don't have a cooler so I dump my fermenter into a bath of cold water, which usually does the job, but this time it took a bit longer.
It's a pale ale made with Maris otter and a bit torrified wheat, and has had a bit of a diacetyl rest - krausen dropped on Saturday (after fermenting from thursday at about 19c) and it's been sat since then at a pretty regular 21/22c. Maybe it needs a bit longer.
I don't think there's owt nasty going on in there as it all looks pretty healthy, and the taste and smell isn't terrible, it's just not quite right.
Anyway. I planned to dry hop anyway, so on top of the 35g goldings I chucked in yesterday, I threw an extra 25g in today. I'm into hoppy pales anyways so that can't harm.
I suppose I'll have to just see what happens now.
Cheers anyways.