What is this vile weed taking over my lawn please?!?!

[MsMontyWomble]

It's growing at a ridiculous rate and has taken over nearly half my garden!!
Does anyone know what it is and how to get rid of it please?!?

TIA

creeping buttercup.
a good feed and regular mowing keeps on top of it.

Thank you! We've tried to mow but it doesn't seem to be stopping it - where it's grown already there is literally no grass left just thick roots from this weed!

So no weed killer as such?

Looks like buttercup

At one time creeping buttercup was invading my flower bed. It comes out quite easily if you have one of those pronged weed tools.