I can't identify this short-ish plant with one white flower with has stacked petals. It also has green, vaguely-heart-shaped leaves that have a pink-burgundy rim, the stalk is also burgundy. I live in England in the East-Midlands, but I'm not sure if this is a native plant or not.
Identifying characteristics for me are the red-tinged leaf borders and stems, the heart-shaped leaves and the pattern of the veins on the leaves. Compare the photograph in my own question about it: What is this (allegedly) mosquito-repellent trailing plant with dark green heart-shaped leaves?
This plant has been mentioned a few times before on this site. In summary, it can be extremely invasive in damp conditions; keep it in a pot if you want it, otherwise be prepared for a difficult battle to control or remove it.