You could try some of the colours from Aubrey Organics (www.aubreyorganics.co.uk; about £11). I haven't used them but they have a good reputation. The results will depend on how grey your hair is -- they say if it's more than 20 per cent grey, you should ask them for special instructions!

My wife swears by Logona Herbal Hair Colours. Unlike nasty chemical colorants, they apparently won't damage the structure or natural colour of your hair. The info on the packet says that "Instead they coat each strand of hair with a strengthening layer that actually adds volume and shine". Give it a go - the colours are fairly comprehensive, from walnut red-brown, flame red, henna red, mahoghany, and sahara, which I think is for blondes. £7.50 for 100g (sufficient to colour shoulder length hair) at www.spiritofnature.co.uk.