I saw a group of these plants in November as part of an event called Sydney Open, one weekend when people can go into buildings that are usually off-limits to the public. (I think Open House London is similar.) The plants were in tubs on the roof of a bank. The leaf sort of reminds me of ‘Christmas Cactus’ (Schlumbergera, Xygocactus) but on steroids — those leaves were half a metre long. And the flowers don’t look like any Christmas Cactus I’ve ever seen.
Pretty, though! And some online searching reveals they might be “Epiphyllum”.