TC1 (Television Centre 1) was (and will be, once the site is redeveloped) the largest of the eight main studios on the site. It's size, and capacity to hold a large audience if required (on retractable seating) made it the studio of choice for large "shiny floor" entertainment shows and flagship BBC output like the annual CHILDREN IN NEED bucket-shake.
It's the front of TC1 that forms the iconic "brick wall" frontage of the centre, sporting the signage and "drawing pin" studs.
The size of the studio was variously described to be as "the largest purpose-built TV studio in the world" or - possibly - "the largest in Europe". There was apparently some doubt whether there was a bigger studio, possibly used for soaps, in Brazil or some such. The "purpose built" caveat is certainly important as film sound stages can certainly be used for TV projects... as can converted warehouses, factories and the like.
The doors were, of course, used to move sets and other items in and out of the studio. At its peak, TVC was a very efficient factory with sets being struck as soon as a production had ended so that another set - for a completely different programme - could be set overnight ready for rehearsals and recording the next day. The beauty of that system, and lengthy rehearsals off-site prior to recording, was that precious studio time could be maximised and the programme shot as quickly as possible... and turfed-out for the next production.
It's hard to get a sense of the height of the doors from the photo... maybe the "Biffa Bin" skip to the right of the shot will help.
I spoke to studio staff who wondered how that efficiency could possibly be retained now that the studios will be at the heart of a residential and hotel complex. Living on top of a iconic TV studio might be trendy but not when you are kept awake every night by noisy tele-folk man-handling sets and equipment all night. If that work has to be done during the day then down-time increases, the facility becomes less efficient and less flexible and, therefore, less competitive compared with rivals located well away from residential areas.