Looks like a cross between a Deutzia and a Viburnum and is in fact a close relative of the former, but from the western USA, rather than Asia. I have it on good authority that this never flowers in the UK - mine evidently haven't been informed.
I have two forms - the 'normal' form, a medium sized shrub with leaves about 2ins across, and a compact form from Larimer Co. Colorado, which has smaller, more textured foliage. Both are flowering at the moment.
I've been keeping them with the other Californians in a relatively open sunny hot place but I now suspect they are better in a moist semi shady situation.
2L pots ~ £12