Even more confusingly, BBC Elstree was formerly an ITV studio centre (The Muppet Show was made there)
In fact a great deal of ATV's output was produced there, and in the 60s had NTSC colour cameras operating in parellel with 405 b/w to produce programmes intended for both sides of the Atlantic.
ATV were 1955 to 1968 the London Weekend, and Midlands Weekday contractor.
Post 1968 the then ITA reorganised the ITV network, and ATV were reduced to Midlands, but 7 days a week.
They built a colour studio centre in Birmingham, but most of their major production continued (out of region) at Elstree.
I think The Golden Shot and Crossroads were the only two major productions shot at Birmingham ? Regional news, and network current affairs and documentaries were Birmingham.
As part of the 1982 franchise round, ATV were forced by the IBA to 'move' Elstree to Nottingham, and change the ownership of the company. Central TV was born. I think the last ATV/Central production at Elstree was Auf Wiedersehen Pet, the first BBC show, Eastenders (or was it Grange Hill) ?