It was definately made at C4 HQ for a period.
I think it always was, I don't remember it being made by anyone else either
I can't see this ending up anywhere other than Glasgow and Manchester - C4 have already got small bases in both cities and surely logical to expand both in areas where there is a media presence than start afresh somewhere new.
Surely that's the point though? It's not just to move it out of London but to try and encourage the creative industries elsewhere.
In that respect Manchester and Glasgow are at a disadvantage. It would certainly be a total waste of time if they went for the boring option and plumped for Manchester/Salford
Birmingham will definitely get something, there's been lot of campaigning to bring it back into the telly landscape.
As for the others, a lot will depend on where the centre of gravity is - Bristol/Birmingham/London will be too southern for example