I'm sure Aaron is correct.
There are a couple of references to this plant in the Forum :
Paul T wrote : February 1st 2011
http://www.srgc.net/forum/index.php?topic=6624.msg182916#msg182916 (photos)
A new purchase for me last week.... a Snail Vine (Vigna caracalla), well named as you can see by the flowers and buds. The flowers start out white and pink, then fade to a yellowy colour. Amazing perfume too, that is just so tropical. Sort of like Lilium crossed with Frangipani, with some other stuff thrown in. Gorgeous!
Meanie wrote on March 8th 2012
Vigna caracalla (Phaseolus caracalla)? I have three that I grew from seed last year which became good sized tubers over the summer. I lifted them in the autumn and put them in pots in the conservatory for the winter, where they are leafing up really nicely now. Hopefully they should bloom this year.