This is Trifolium repens or White/Dutch clover. The 'trifolium' bit means 'three-leaved' and 'repens' means creeping (the stems are stoloniferous). It is common in lawns and verges where soil fertility is reasonably high (and therefore species variety is low). Bees visit for nectar so don't rush out to mow them all off.
Being a member of the pea family they also fix nitrogen in their root nodules.