Lardy balls.

That is what they are called in Shropshire.

More formally they are Snowberries.  Symphoricarpos albus.

A shrub introduced into Britain in 1817. Widely planted and naturalised.
The flowers are pink and very small. It is best known for its marble sized white berries.
It is said that if you tread on them they give a loud pop, but I did not try it.