Marsdenia oreophila (Cionura oreophila hort)

Cionura oreophila is a rare evergreen climber of the milkweed family, like the other milkweeds it has scented flowers (Waxy white)  although to my nose this is both the strongest and sweetest scent of the group. Not fully hardy (min -5c) but worth trying on sunny sheltered walls or in the conservatory where its scent is even more strongly noticed. 

Marsdenia oreophila is a native of SW China, in Yunnan, where it apparently grows in hedges and scrub, flowering in May–August. Stems to 2m higher on a warm wall; leaves to 6cm long. Flowers 1cm across, in umbels of around 10. For any good soil with ample water in summer, drier in winter.