well they like lots of slugs and snails. so dont over do the slug pellets. I have them in and around the garden but rarely see them, just their spoors. I have log piles for them too in out of the way places.

Tidy and weed free gardens dont get Hedgehogs. If there are no weedy undisturbed untidy corners, they can visit, There is nothing for them. Weed killlers too may have made us all too unnatural.. That's a good excuse for being lazy.

As far as I know, there also needs to be gaps in the boundaries for them to get through. There are also 'hedgehog houses' for sale now, though I bet it is not hard to construct them yourself. And no slug pellets.

Edit: found some interesting info here including instructions on how to make a hedgehog house:
http://www.rspb.org.uk/advice/gardening/homes_for_mammals/hedgehogs.asp

Recently I asked the hedgehog rescue stand at the Malvern show about this and got the following answer -

Yes, gaps in fences or hedges are essential for free wandering.
Rescue hogs are only placed in areas where there is a known established population of hogs already, which probably means a no for us, sadly. In 4 years here I've not seen a single one, though I've spent a large chunk of my time in the garden and they would love it. Don't know about the connection with badgers as I've never seen any of them here either...
Unfortunately these are hard times for hogs.

well firstly you probably do get hedgehogs and secondly the badgers are opertunist omnivours and may predate on hedgehogs .not saying they do but if anything is powerfull enough and clever enough to work out how to get to that meal inside the spikes its a badger.you could put some dog food out for them like pal or something but i guess the badgers would eat it .you dont very often get mice and rats together as rats love eating mice.