There are a number of references upthread to the DoubleTree Bath Road, often the cheapest Hilton group option. This is closing in the next day or two, and those booked moved to other hotels. In the case of Diamonds, it's the T5 Hilton, so an upgrade but for the travel issues. The hotel is being switched to "Exclusive Use to HMG", (Home Office in other words) and I suspect that answers the recent query about The Atrium. Typically when this happens the hotel will be out of service for many months.

EDIT: I've put quite a few more details in the main thread for this hotel in the Hilton forum.