I think it looks like an Oxalis,but not certain.Someone else will definitely know..

Hi
Christia vespertilionis Red Butterfly Wing
Have a look on this website and he has all the info that you need I am currently bidding for some seeds on ebay from the same site
http://www.strangewonderfulthings.com/List.htm
Steve

Whilst this pic does indeed make the plant look like a Christia, it is, as Bloomer suspected, actually an Oxalis, specifically Oxalis triangularis - see pic & info below:

http://en.wikipedia.org/wiki/Oxalis_triangularis

Yes, definitely Oxalis, with its leaves folded back - hence the confusion. It's tender, so in Scotland will need to be indoors for the winter.

I agree, Oxalis triangularis. We're selling a lot at work right now.

Thanks.