I looked at different types of pipe and found this in Toolstation which I bought to use and I think it would probably work ok but my girlfriend then suggested using a plant pot with the bottom cut out (she had some fairly straight-sided ones, bottom hole 12 cm wide).
The first version the cats still managed to squeeze through so I then taped another plant pot inside the first but sticking out more and this now prevents the cats getting in, although some still try. The cats were scooching in far enough to reach the food but with their back legs still outside so they could drag themselves out backwards. I found the trick is to make the pipe/pot just long enough to make it impossible for them to reach the food. I think some of the more slinky ones could actually still get in but they would have to go all the way in and are intelligent enough to know they may have difficulty getting out again.
I used loads of Gorilla tape to attach the plant pots to the transparent storage box then weighed it down with a heavy fire brick so it couldn’t be moved. I set up 2 wildlife cameras and found out I have a resident hedgy living under our decking so I put the feeding station near the den hole. It’s been working great for the last 2 weeks, the hedgy comes out every night and I get several video clips of it feeding and drinking (wow do they drink!).
There is no obvious way into our garden so I’m not sure how it got in but I have now cut a hole in the fence so it can roam more easily, then a couple of nights ago another hedgehog arrived and tried to get into the feeding station but couldn’t because our resident was already in it. We live in a built up area in Newcastle upon Tyne so I’ve tried my best to make the garden more hedgehog friendly and so far it seems to be paying off.
I’ve made a sort of video collection/diary of my efforts but can’t see a way to upload video or attach pictures to a post so if it’s ok with the admins I’ll put a link to my Youtube channel (I’m not selling anything or advertising anything, it’s just camera clips)