North facing's a good situation for lots of plants, but where you are in the UK makes a difference... and when you say small, how small? Measurements? Anything in it already?

Thank you I have updated my original question.

So I see - not sure how near the coast you are, but if within 15 miles, it'll be milder in the winter, if further in, I'm assuming it can get pretty cold. Don't know what you've got already, but here's a few ideas:perennials: Achillea, Armeria, Bergenia, Hesperis, Iris, Primula, Pulmonaria, Sempervivum, Coreopsis, Ajuga reptans, Campanula varieties, Eryngium. Shrubs: Euonymus varieties, Leucothoe, Buddleia, Berberis varieties, Sambucus, Tamarix, Kalmia, Lavender in sunnier spot, Yucca, Prunus Otto Luyken, Mahonia aquifolium, Cornus alba 'elegantissima'

If you want bright flowers you can't do better than perennial geraniums. You can get all shades of pink, lovely bright blue and a few white. You can get quite tall ones, that tend to flop over and fill lots of space, neat ones like geranium sanguinium that make a mound and flowers all summer, and prostrate ones that are small in winter but send out long flower shoots in the growing season. Check flowering times when you buy as some flower for longer than others.
Doronicum produces tall yellow daisy like flowers in late April. Try early primroses and daffodils for Spring, and in summer try the little fibrous rooted begonias that you can buy in trays for bedding at this time of year. They flower all summer and tolerate dry or very wet weather. They prefer shade or semi shade. Do not plant too near your hedge as privet is very greedy and the soil will be very dry and lacking in nourishment just there.