Although much of his quest for openness involves the public - there will be big public areas within the new and old building, with the famous Radio Theatre opened up to the new courtyard, where live open-air performances are planned - much involves the BBC’s own famously hermetic departments. The new building is designed around a notion of common break-out spaces, even including specially large landings on the stairs, where members of different departments can stop and talk rather than scuttling past each other in corridors. Views are created by making big vertical slots through the floors. The BBC staff and contributors - around 3,500 of them at any one time - will often be on public view. The back of the original Broadcasting House is revealed via a full-height glass slot traversed by bridges. The whole place becomes a great deal less introverted, less fortress-like. For all that it is stuffed with studios across the back, it will become much less the closed institution, much more the public cultural attraction. In a way, this echoes what happened to another elite institution, the Royal Opera House in Covent Garden, which gave itself a new public face when it rebuilt.

Other strategies are at play, however. The BBC’s director of finance and property, John Smith, maintains that good architecture plays a part in attracting and keeping the talent the BBC needs. For him, the low point of the BBC estate came in the late 1980s when the only criterion was low-cost accommodation and a grim new office block was built at White City, which everyone hates. Smith has accordingly gone in the other direction, has actively sought out good architects through competition, and established a financial package with developer Land Securities that will spread the cost of this huge rebuilding programme over 30 years. “The nation’s broadcaster ought to produce buildings the nation can be proud of,” is how he puts it. And if New Broadcasting House is inevitably expensive, it will at any rate reduce the BBC’s stock of buildings by one - since in 2008 the lease runs out on Bush House in the Aldwych, long home of the World Service.

For all the public accessibility, however, the most enduring image of the new building will be the televised one of the great newsroom in the basement. MacCormac makes this unashamedly dramatic, drawing the whole weight of the building down onto branching arms rising from a few fat columns, like Tolkienesque trees. Daylight will flood down from above. All news, in whatever format, will emanate from here. It will thus become the image of the BBC, broadcast around the world. Few architects ever get that kind of continuing publicity.