Starting to get calls from people concerned about small hedgehogs in their gardens. Hedgehogs of any size who are seen wandering during the day are very likely to be unwell in some way. In this case, the best thing to do is to capture the hedgehog (use gloves to avoid being scratched by its spines) and confine it in a box before telephoning the RSPCA control centre 0300 1234 999. They will do their best to arrange for the hedgehog to be collected and taken to the closest RSPCA wildlife centre. (In our case, this is East Winch, in Norfolk). I suggest you put the box somewhere where any insect life will not be a problem, such as a garden shed.
Very small hedgehogs who appear in the garden after dusk are probably not yet at risk because there is lots of wild food about still (the slugs in my garden are so fit they scare my cats!). If you want to improve their chances of surviving their first hibernation by providing extra rations (or just want to encourage them closer), you can get dried food made specially for hedgehogs from most pet shops. Being mammals, hedgehogs can produce their own body heat, so the unusually chilly summer isn't a problem for them in the way it is for cold blooded hibernators like tortoises, or really tiny mammals, such as bats. That means that, for the moment, they're really best left where they are rather than taking up space in a wildlife hospital that may be needed by another animal.