“Most of the blocks planned on a north to south axis (the outlook from which is either to the east or the west) have flats on either side of a central corridor. This is an economical solution as it reduces the number of lifts which need to be provided in these buildings. The block next to Moor Lane, which has a poor outlook to the east for residential accommodation, is planned with up-and-over maisonnettes so that at least the living room of each dwelling overlooks the gardens in the centre of the scheme.”
Chamberlin, Powell & Bon, Architects “Barbican Redevelopment” April 1959
Willoughby House is “the block next to Moor Lane” with the dreadful view towards the east, referred to in the quotation above.
In Willoughby House the layout of the flats was so contrived that all living rooms face west, over the gardens and lake.

Images taken from the City’s original letting brochure for Willoughby House
The block has central corridors for every two floors. Whichever way the flat’s main door faces onto the corridor, the flats are fitted together in a scissors formation with stairs down or up so that the living room always faces into the Barbican. In fact, the view east now isn’t so bad – it’s occupied by Britannic House.