According to the Gardeners World website, Akebia quinata isn't hardy. Your trench seems on the small side for a plant that you can expect to grow very large. Pity as it looks gorgeous. You could always try it and prove me wrong. :-)

Akebia quinata is usually hardy in London, though, Beattie, unless in a very exposed area. What worries me is that you appear to be saying the depth of soil would only be 8 inches? If that's correct, no climber will do well there. As for the partial shade/sun thing, I have grown it successfully in a pretty shady position and its romped away with no trouble, though the flowering was less prolific.

Akebia quinata is Chocolate vine? Yes? 'Cos ours has not only survived last winter, it is now 14 years old and believe me, we are exposed.
Agree about the soil depth though, nowhere near deep enopugh for anything except perhaps a well fed annual climber.

HI Thanks for all your responses , the trench is likely to be much deeper as its just an exposed area from the footings dug for the wall. so goes right into the earth ... I may just give it a go for good luck. It will be very protected there ... who knows.. it may grow to like it!

thanks lg

Well if you're saying its just an open trench with soil beneath, it should be absolutely fine.

Pity you are not near enough to come and take some of the hundred or so self layered bits from ours.