I have 2 of the Flowering shrub expert books and it's not in either!
When we wanted to fill the garden someone recommended a retired policeman  that grew lots of things, and he sold them all at 30p  and it came from him. The only one that was named at the time was the Amelanchier, they were all "shoots with roots" as he called them, and I had to identify them afterwards. he told me when they flowered and that was it, so they were numbered  instead!!
I've found 2 that look very much like mine, one is Zenobia (wrong soil) and the nearest one is Blueberries, but never had a blueberry just lots of blossom.
I'll see if I can find the pics and let you know!
I googled white bell shaped blooms! there's only 48,000smiley: eek!!