Passiflora tetrandra. Very rare and unusual Passiflora from New Zealand with tiny flowers. Dr Reto Gamma comments, 'P. tetrandra seems to be closely related to Astrophea, furthermore, it is quite tough and survived the coldest winter in 30 years without any protection in Southern England.' I totally agree. It will keep its leaves when other nearby Passiflora are defoliated by the cold.
It is unique amongst Passiflora in that plants are either male (usually four stamen) or female with flowers to match. My plant, grown outdoors, has flowered for the first time after five years - I am sure the hottest April ever recorded in UK has triggered it. The fruit are edible, an edible gum can be extracted from the stems and a fragrant body oil from the seeds. (From PFAF.)