In article , Mick writes
I have just seeded a large lawn just out side Cambridge , and have been
swamped with a weed that I need to eradicate .
It grows very quickly and can form a hummock in 3/4 weeks , it has Geranium
type leaves and flowers bluish .

If not one of the wild cranesbill species (G. pratense is the one with
obviously blue flowers), or a naturalised species, it could be one of
the weedy mallows (for photographs see sig.) which have leaves that can
be mistaken for cranesbill leaves on a cursory glance.

A hummock-forming habit sounds more like Geranium than Malva.
--
Stewart Robert Hinsley
http://www.meden.demon.co.uk/Malvace...a/gallery.html