Is it in the border or the lawn? Please could you add a photo and if not a description of the shape of the leaves and the flowers?

I'm guessing Oxalis corniculata, Procumbent yellow-sorrel. Hard to eradicate as it spreads via tiny bulbils.

I was thinking possibly Prunella vulgaris, selfheal as it has purple flowers.

if in the lawn then in spring the weed & feed type lawn treatment will work given time.

if in the borders then it can be dug out or killed with a weedkiller. personally I do the digging routine.

But the sorrel has yellow flowers and self heal doesn't really look like clover. The latter can be dug out of borders and treated with lawn weed killer in the lawn. Really do need a photo.

Oops Sbg, just realised you said most of this already...

I don't mind having some clover mixed into my lawn. I have some purple, some white. Just not something that bother's me.

you'd be amazed at how many people say they do look like clover. then when you show them clover next to it they go 'oh yes not like it really'.
a photo would be ideal.

I wouldn't be surprised Sbg... in spite of the fact that lawn clover is usually white. I've never seen purple clover in a lawn have you, but I do have some very insistent self heal - its quite pretty really. And dog violets. But nobody critical looks at our lawns. Its the hawkweed that gets to me lol. Perfect lawns and the countryside don't mix very well.

I have purple clover & white. The bees really like it (clover honey is extremely popular).

All our varieties of purple clover are rather too tall to survive in lawns - you must have a different variety.

non white clover is more of a red / pink really rather than purple.

onw of the white ones is short enough to miss a high cut but my oh usually goes quite close. he has got most of it out now except for a few spots that he leaves for the bees.

Well done that man - quite an achievement!