Hi there
I think this is Symphoricarpos albus.( Commonly known as the 'Snowberry').
It's a deciduous shrub with white berries like marbles,as you say, from
mid-autumn to mid-winter. It's also meant to have pink flowers from
mid-summer to early autumn. Expected height and spread:-6ft by 6ft.In one of
my gardening books, it's listed under plants that prefer shade. I remember
it as a kid as we used to squash the berries.
Hope this helps.
Liz