Exploding plant

I'm curious to know what this is.

I came across loads of then whilst out on my lunchtime  ramble.
If you get too close to them and disturb them,  the seed pods explode and shower you will little seeds.

They may be classed as weeds - a) because of where I saw them and b) because of the blanket nature in which they had colonised a rough patch of ground.

Any ideas of their name?