Helianthemums would fit the bill - you can get them in various colours ranging from cream to red, and they're evergreen too. I take the shears to mine when the first flush of flowers ends, and they flower again.

Geranium springs to mind they come in a variety of size, shape and colour , take your pick!.

They are a good choice, but not many are evergreen.

Sorry didnt know evergreen was a consideration, how about the many coloured hucheras or euonymus.

Campanula are very good for attractive ground-cover and are attractive, especially when in flower. I recommend 'Dalmatian bellflower' - a campanula with light blue/violet flowers that keeps on flowering.

There are many sedums, and they are evergreen.

I'd go with Helianthemum, very good in full sun, remain evergreen - Ophiopogon nigrescens is another option, along with Arabis ferdinandi coburgi, and Oreganum aureum makes a really good yellow leaved ground cover in that situation, Also Campanula muralis. All retain leaves during winter.

I just let nasturtiums run riot to fill blanks.

But nasturtiums are only there for a few months. They're late starters - don't get going til late spring / summer and riot til the frost kills them.

Thank you everyone - a lovely selection to choose from!

Don't forget London Pride.