There are some Ericas which will do well there - the European, autumn/winter flowering ones tolerate lime. Have a look at Erica manipuliflora, E. manipuliflora anthura 'Heaven Scent', and E. x vagans. Campula portenschlagiana will provide flowers in summer, and remains a neat green hummock all winter. Helianthemums, which flower in spring for quite a long period, also remain evergreen during winter, but they will need a good half a day of sun.

Hi Bamboo,
Thanks for giving me some ideas. I have looked them up and quite like the campanula, I have a Helianthemum in the rockery but it tends to go woody. The Erica sounds good too if I can find any in my local garden centre. :)

Helianthemum should be clipped over after its more or less finished flowering, taking a good couple of inches all over. More, if necessary.
I forgot to mention Erica darlayensis - those varieties should be okay in that soil as well.

there are the lamiums [dead nettles] some have beautiful silvery/green foliage with flowers in pinks white and yellow. if the site is shady then there are ajugas [bugles] and again a range of leaf colours. some Heucheras too would fit the bill. All of these are evergreen and fully hardy. They grow in my chalky soil really well.

There are also epimediums which flower early in the spring. They are tough little plants and once established, no weed will ever grow through them

Would winter aconites tolerate the lime soil? They like a dry soil in summer, which the terrace would provide. You could also try some creeping phlox which are unfussy about soil PH, and they are evergreen too. Snowdrops, japanese anemones and various creeping thymes may also be an option.

Most Ericas are acid loving, though as Bamboo has said Erica darlayensis will tolerate lime (tolerate does not equate tothrive). Ericas can also get ugly quite quickly if left untrimmed. I would go with Campanula and a simple mix of Hebe can look great as you get different colours, heights and shapes.

At the risk of boring everyone rigid by reiterating my hatred of the stuff, NEVER be tempted to plant Vinca (periwinkle), it looks lovely for a while but it's the most appalling thug, and you'll never get rid of it. I'm taking a flamethrower to my rockery once the snow has melted. It's travelled everywhere, including yards into my lawn, and downwards, too, and there's no stopping it.
We have quite limey soil, and various bulbs and cyclamen provide some colour, and ajugas, as Seaburn Girl says, do really well, and provide a bright note, but beware, these too can be a little invasive if you don't watch out.

Thanks everyone, this gives me plenty of things to try :)