Posted: 17/01/2016 at 12:35
Hi Lisa - as you already have Pieris and Camellias, you should find Rhododendrons and Azaleas will probably thrive. There are loads of varieties readily available. I also have Mahonia in a similar position - also clay soil. They are prickly but if that's an issue, you can plant in front of them if there's sufficient room. Hollies will do the same. Skimmias and Gaultherias will also do well.
You could also try Osmanthus burkwoodii - it has scented white flowers in late winter/spring, and Sarcococca - Christmas Box. You could add a few foliage evergreens like Euonymous and Elaeagnus as well - several good varieties and easy to find.
Those are all evergreen, but you could add a few other deciduous shrubs into the mix - Viburnums for instance - although there are a few evergreen varieties of those too.