Thanks for the advice
I managed to have a look in his nest (much to his unhappiness as he shot through to the other room in his house and wouldn't come back until I went away!) and it does looks like he's been pouching everything from his bowl and sticking it in his nest. Not peeing on it thankfully but I'm wondering if he's even eating anything at all. I did wonder if maybe the house would just be encouraging him to hide so I'll maybe give him another week and then change his house to something more open like you suggested.
His cage is this one
https://www.amazon.co.uk/Little-Frie...grosvenor+cage. We've put a bit cardboard in it to make it a bit smaller lengthwise (not sure if that will help or not or if getting a smaller cage would be better) and I've moved his food bowl from the top of his house to the cardboard and he's ventured to it to pouch and run back so at least he's going a bit further than the roof of his house
He's not in the room with Boris and Pasha yet either, we were going to move him through there at the weekend but was wondering if he would be best staying where he is until he's a bit more settled?
Sorry for the rambling post lol.