Invasive weed but what is it?

Googled until my eyeballs are popping but cannot identify and therefore eradicate safely.



I had a suggestion that it's chickweed but the leaves on my unknown weed don't show any signs of being furry/hairy.
Also the flowers are never white, always a purply black and they don't open up as 'normal' flowers.
It never grows higher than an inch or so.
Although it shares some properties with chickweed there aren't enough to convince me it's the same plant.

 

I'm sort of tempted to agree with you Marley but the leaf shape doesn't match. Also perhaps I was wrong about the hairy bit - if you look closely there are some hairs on the leaf edge of my weed but not on the viola.
My (limited) experience of viola tricolour is that it's quite a pretty weed and grows pretty quickly above the grass level.
I'll let some grow for a couple of weeks and come back with a better picture.

 

It justmay be that the recent continuous wet weather has exacerbated the situationsince it is ubiquitous over the gressed area. Not 100% of the area but patches spread all over.
Like your sig. :-)

 

Nearer, Marley. 'Cept for the flowers but leaves look superficially similar.
Wait for some growth and hopefully then we'll see.

 

I would have said Selfheal. Seems to be rampant this year.

 

I can't really argue Boghopper but leaves and flowers don't match. Yet.

 

O.K. Found it!
Prunella vulgaris / Selfheal/ All Heal

Got a larger sample from a neighbour's lawn:



Thanks guys for your suggestions. The answer seems to be Vitax Lawn Clear.