French Lavender (Lavandula stoechas) cultivars are very popular? http://www.thompson-morgan.com/seeds1/product/9537/1.html They vary in size and compactness but with a light pruning every summer would make an excellent, low, evergreen hedge. Also quite a few Vaccinium species are low growing (some as low as 20cm) and evergreen. Vaccinium crassifolium Wells Delight is named the Creeping Blueberry as it produces edible fruit. Vaccinium vitis-idaea (Cowberry) grows to 25cm high and produces red edible (although not very tasty) fruits. Berberis x stenophylla Corallina Compacta is an RHS award winning evergreen shrub which only grows to 30cm height and spread! As an added bonus it also produces masses of yellow-orange flowers in early summer. Its also worth looking at Jasminum parkeri which only grows to about 30cm high and produces yellow flowers in the summer.