Hedgehog populations have declined by a quarter over the past decade and they need help. You can help by providing suitable shelter and supplementing their natural diet of slugs, snails, beetles, worms, caterpillars and suchlike with some protein (e.g. meat based pet food, minced meat or crunchy hedgehog/cat biscuits), particularly in periods of unseasonable weather. You could also provide a bowl of drinking water (not milk) at several sites around the garden.
For more information about hedgehogs, please visit the British Hedgehog Preservation Society website here and/or the Hedgehog Street website here.