In reply to aln:
I can't remember if it has a forum. The Gardeners World website does. As far as the website goes I suggested looking at it because it gives lots of information on just about every plant you can grow in Britain.
Reading your description of the area you want to put plants in I think it sounds good. You should get plenty of Sun in the morning and some in the afternoon. You'll not get any frost so you can plant some exotic stuff, someone suggested orchids earlier which could be good. As you're planting in containers you can use whatever soil suits the plants you choose. Could you plant climbers to make use of the height? Honeysuckle would give a nice scent and clematis will give a spectacular display of flowers in the Summer. Cacti would also be interesting, Christmas cactus produces flowers at Christmas so would give a bit of mid winter colour, plus they're as tough as old boots. I've got one outside on my windowsill and it stays there over the winter. Otherwise think about getting something evergreen or maybe even a dogwood or two which would add some bright red, yellow or green in winter.
The other thing I've tried to do when selecting plants is to make sure you've got something happening for as long as possible. One easy way of doing that is to start with a few plants but when you need a bit of colour have a look around your garden centre for something suitable that's about to flower. Over a few years you'll build up a nice collection that should blend well.