Little blue flower

This little flower is very pretty but unfortunately spreads all over the garden.  Once flowered the seed head suddenly pops and the seeds fly all over and in no time at all new plants appear.  Anyone know what it is called?
After tea had a quick walk around the back paths and then across the field - don't think many have been recently as the grass in very much overgrown.  just noticed this decaying tree trunk which, when we got nearer appeared to have been pecked  numerous times by I am presuming a woodpecker