This section of the garden represents something like my ideal of a layered, successional woodland planting or more accurately edge of woodland. London gardens are often well suited to a woodland edge selection of plants. Invariably there is the shade of mature trees and surrounding buildings but also a good amount of sun for part of the day. 

 The meeting of open ground and forest (or glades within a forest) is a productive habitat in nature- the flora and fauna get something of the best of both worlds. So from the design point of view these are the plants to choose.

 Plants that like or tolerate shade tend to flower earlier in the year to take advantage of the light before the the tree canopy leafs up. Therefore late winter to early summer is the peak flowering period though there's plenty of greenery into autumn and a few plants that will flower deeper into summer.

 The trick is to select plants that come on as others fade start to fade. This is achieved by a mix of bulbs and perennials that clump or spread. Self-seeders -particularly biennials- fill any patches of bare soil. Climbers can be used to good effect if they have something to cling on to.

 By careful selection different species (often from different parts of the world) intermingle and co-exist. In a sense this mimics a natural ecosystem. Nature is sometimes perceived as chaotic. In fact nature is orderly on a colossal scale. It's possible to tune in to that natural order albeit on a smaller scale in a garden.