Hows about Lavenders, grasses (smallish ones) or heuchera which doesn't grow too big and gives winter interest. Fox gloves, Alluims and Lupins push up through other plants so planting not a huge issue. Watch for slugs and snals with the Lupins though!!

Aubretia is wonderful in clumps and round edges. Strikes cuttings easy, stays green over winter. Easy to control. Penstemons do not vanish completely either. Small evergreen shrubs dotted about...good idea. Deciduous shrubs too, like the bright leaved spireas for Spring colour. Heleniums...lovely bright colours. Easy to grow and separate to make more lovely bright clumps. Not vulnerable to slugs....as far as I can see. Hardy fuschias too...but need to be cut right back to keep under control. Any bare patches left have fun with tulips and other bulbs that can be left in. Day lillies are long lasting....not too prey to slugs. Fans can be split and given away or clumps downsized. Arrange to taste. Also look up plants that have a winter interest in their seed cases too, such as eryngiums.

Thats brilliant Dorjac & Lulu33! Thanks so much, I love the idea of grasses and i've been looking at 'rave on' heuchera. I love the lime green spireas so i'm definately going to go for one of those too. I also had the idea of putting in various herbs which I think might work quite nicely. Thanks again, you've been really helpful.