Yes Hugh, the big trees are a weeping willow, medlar and a robinia, then there are about dozen evergreen shrubs and a couple of deciduous shrubs. Spring time isn't a problem, in fact, I have a wonderful show of foxgloves, nigella, bluebells, hyancinths, azaleas, poppies, geraniums, aquilegias and crocus. The thing is, as the leaf cover becomes more dense, and the ground becomes more dry, and these plants naturally finish, I am left with foliage and clear ground. I do have a selection of grasses which don't seem to mind the shade and do look splendid at the moment, and I do have a dozen or so small ferns, but they are still small and are going to take a couple of years to look stunning.
I shall definately get some autumn flowering cyclamen and wood anemones. Thanks for the advice, I sense the cheque book might have to take a battering to help colour up this gap.