Which white campanula is this please?

Can anyone identify this for me, or rather for the friend who took the photo below?

I'd suggested campanula carpatica weisse clips/ white clips, but on closer inspection the flowers look rather longer - and the stems taller?

She'd love to know what it is so that she can track some plants down for herself



A detail:

Many thanks everybody!

 

OK answering my own question I think it's probably Campanula poscharskyana 'E.H. Frost'

 

Hopefully, if that's what it is, it won't be as thuggish as it's blue relative @Clare G

Nice little plant though.

 

I quite like the blue one myself @fairygirl - I've got it happily growing away on a rubble bank where it does well and is not a nuisance. Am ruthless about not letting it colonise the flower beds however

 

Presume pic here/above is the one from Beth Chatto site.
Leaves seem very different to those in your original post.
Leaves above are jagged.

Campanula poscharskyana frost - The Beth Chatto Gardens

Campanula are not easy to id.