I thought it was Crinodendron hookerianum, the Chile lantern tree. If it is, I would think it would be a sizeable shrub/tree. If you must, then a trim after flowering.

I think its Crinodendron as well - and it gets up to 6 metres high and wide, so its not overgrown at all. It may, though, be planted in the wrong place... needs much more space than its got there, but does require plenty of shade and in soil that doesn't dry out frequently.

How lovely, what a find, definitely a Crinodendron hookerianum, I have molly-coddled and nurtured one for ages and it is now in the garden and will hopefully now romp away. Most things want more space and if we all only had a field or two to give them the room they would like - wouldn't it be lovely? But they do like shade and require a lime free soil, so I am hoping for the best.