Mirabilis? (though that's an un-confident guess!)

I agree mirabilis. Flowers are nice but completely takes over if you let the seeds drop. Still popping up in my garden after 8 years. I dig them up and compost, before they bloom.

Has it flowered yet Melchi? Mine used to have different coloured flowers on the one plant . . . in the afternoons! Its other name is the 4 o'clock plant.

Thank you Sheila and Littlelegs. I have conveyed the info to my son. I have to say that it sounds rather nice!

It hasn't flowered yet, Sheila. They have just moved to a new home with not much in the garden, and things are just beginning to reveal themselves. It's their first garden as well, so it's all quite exciting.