The old Hummingbird/tropical bird House was between the Bird House and the Wolf enclosure, where the squirrel monkeys are now. It was a fairly small brick building with a glass roof. There was a central path and a shallow moat on each side, separating the public from some fairly thick vegetation. It had a range of small tropical softbills, although I can't remember hummingbirds there in the early '70s when I visited Regent's Park quite regularly. The birds I do remember are blue-backed manakins which bred there.
At that time, several UK zoos and bird gardens had free-flying hummers. Chester had some in the small mammal house. The old Birdland at Bourton in the Water had several walk-through tropical houses with hummingbirds (and one with red birds of paradise if my memory is correct).
Alan