It took a while to track this one down. The way I did it in the end was to type in a loose description of the plant into Google Images and look for a picture that matched. “bell like orange flowers succulent” did the trick.
From what I could find these plants are a native of Madagascar. A previous owner of the house or a neighbor must have liked them, they are running wild all through our garden.
Noticed belongs to the order Saxifragales, I wonder if this is where the character Saxifrage Russell from Kim Stanley Robinson’s Mars trillogy got his name.