In the deepest shade how about a couple of ferns and a Brunnera Jack Frost, or there's a more recent variety with more white on it. There seems to be a young tree right at the back - what is it, and does the sun shine on the top of it when the ground is shaded? Is the shadow much longer in the winter? If you get sun for longer in the summer you could have a couple of perennials that flower in the middle of the summer and then die back? You might be fed up with me always recommending Euonymus fortunii but there's nothing like it that I can think of that looks bright all year and needs very little care - just a light clip if it gets too big for its space.
And it contrasts well with ferns - you can get ones that don't die back in winter too. Anemone blanda and Anemone nemorosa would probablyboth be happy.

Sarcococca is a nice evergreen shrub with sweet scented flowers in the depths of winter. I also have a white and green Euonymus in deep shade to brighten the area up. lots of ferns such as the native harts tongue is a mid green and keeps its foliage.

look at shade plants by scrolling down to the bottom, where you will find the alphabet. click s then shade for ideas.

Thanks Steragram and Seaburngirl I'm going to look at all suggested.

Skimmias will work there - you'd need a male and a female to get berries though, unless you get S. reevesiana which is an hermaphrodite and will produce both flowers and berries.