I was going to suggest Aster x frikartii Monch last night, the closer photo suggests it
might be. There are others which look very similar! Height and flowering season can help but isn't reliable due to different climates and soil conditions.
http://www.whiteflowerfarm.com...
http://www.rhs.org.uk/Gardens/...
Aster amellus 'King George' is similar ..
http://apps.rhs.org.uk/plantse...
Growth habit, such as whether it's lax or upright, and leaf shape may help. According to the next site, Monch has a slightly lax habit where King George is upright according to the RHS. Monch is an old and reliable variety, I'm leaning towards that.
http://www.saga.co.uk/lifestyl...
