Did the rounds today, visited all the places (not Cash Providers on Magdalen Street which I mentioned though, it didn't look appropriate at all) and left flyers. Cash converters on Plumstead Road (presumably this applies to the one on St Benedicts Street too) were adamant they wouldn't take a bike (or anything? can't remember) from someone without ID, so a thief wouldn't do that. Or if he did he'd be giving himself up. Although false ID isn't impossible.
I asked in Next about CCTV. They said none of their cameras show outside. I didn't ask in McDonalds for some reason. I may phone them or write to them. I did notice a CCTV camera, two actually, on the side of the, I forget its name, something like TV and Film shop, looking onto the square that the library looks on to, up from the bike racks where my bike was. I asked in there, they pointed me to an office in the library building but to the right of the library before you go into the library. The guy said it doesn't show any of the square. I'm not convinced. He was monumentally unhelpful. Except he did say the police have a CCTV camera looking onto the square in front of the library. And sure enough, they do. Right up on the corner of their building looking down onto the library square. It would only see the top end of the bike racks, I locked my bike at the bottom end (that end would be obscured by the church), but if the thief went up the hill after getting the bike rather than the other way, he'd be seen by the police camera I think. So maybe I should ask the police?!
I did come across this in my various searches:
So the police do follow bike thefts up sometimes. Quite similar that story. Norwich centre, early/mid afternoon, a Cannondale.
Anyway, thanks for the help.