Thank you so much for your reply Nic.
It looks like the sonic repellers are definitely out of the question then, I’m glad I asked and haven’t wasted any money. I used to keep (fancy) rats many years ago, so know how clever they are and my husband would freak out if he knew my ‘little garden secret’ before I’ve outwitted them as he’s terrified of them! The little monkeys take food out of the dish while the hedgehogs are actually eating. Last night I tried moving the dishes more into the open, rather than inside the ‘feeding station’ (a plastic wendy house to provide shelter and to stop the food getting soggy), but the rats stole the food even faster. The cat biscuit trick you mentioned is definitely worth a try, I have three cats so have plenty.
I do feed the birds too I’m afraid, and have taken to taping down the lids on the feeders overnight, as my little furry visitors were hanging upside down, lifting the lids, and helping themselves to the sunflower hearts. It took me ages to encourage goldfinches to visit the garden, so am a bit reluctant to stop feeding them (although I know that isn’t helping my problem). I might try reducing the selection I leave out though and not top up as often.
I’ll have a look at the link you posted later (I’m at work at the moment) and see if there are any more handy tips.
Many thanks again for your help, it’s much appreciated.