Its an oxalis not a clover and a lot of people would like to know how to get rid of it! Just pull it out wherever you see it, don't let it seed as it throws its seed rather than just dropping it and if its somewhere suitable you could try weedkillering it. But in the lawn have you tried Weed and Feed or Weedol?
Its popular name is Sleeping Beauty.

try black medic

Medicago lupulina or black medic is a member of the clover family and is certainly has a little yellow clover flower. It is a common weed of lawns. we have had it and it took 3 applications of feed and weed lawn treatment and time.

Medicago lupulina is a little yellow clover flower common name black medic. feed and weed lawn treatment will work but you will need several applications.

sorry about the multiple comments but it didn't seem to be loading but it was oops :o)

Black medic doesn't have red leaves though and I thought that's what Kat meant by red clover as the flowers aren't red. If the flowers grow in a sort of tuft it will be a clover but if they are tiny and more or less star shaped it will be what I suggested.

ha I see stera,I read it as the red clover plant [ie going by the leaves] but it has yellow flowers. There are several yellow clovers ie Trifolium too.
we will have to wait for Kat to get back to her question. ;o)