I have planted Carex ‘Evergold’ in one of the small, square beds set into the gravel and I think flowers would be interesting standing up above the grass. This is the ‘hot colours’ part of the garden and so I think quite a dramatic combination could work well: Astrantia, Sanguisorba, or a purple Sedum.

Sounds a good planting combination!
Thank you – it is quite worrying in such a small garden. The colours have to be harmonious, and above all the plants have to fit into the space. I took cuttings when I dug up the heleniums in August, and will replant amongst the Graham Thomas roses and Carex Testacea in the spring. So reds amongst the nearby yellow-variegated grasses should work in colours. Would you care to talk plants in London?