Looks like an oxalis - possibly o. debilis.

Wagger many thanks, my mum had this as a cutting many years ago , she now lives in a flat and my sister dug the plant up and put it in her garden, it is so pretty and i keep trying to get one but never seem able to find it!!

I've never seen this for sale in all the years I've been working as a gardener - its probably because its considered an invasive weed, so dig up a bit of your sister's if you want some. That's how I got mine years ago, from someone else. I don't have it now though, would quite like some... has little bulbils at the base, so dig deep enough to get those.

Bamboo that's exactly what i have done, my mum is going to take a bit off for me

yes does look like Oxalis there are new cultivars out with different colour flowers that are also quite pretty.