I best thing you could do would be to talk with the owners, or whoever is in charge about proper chin care. I would make sure they actually know the living conditions are not good for a chin, they may not know. Some people honestly don't know that chins shouldn't be kept outside. There is a ton of bad info online and that seems to be where a lot of people get their info. Also being a farm, they may think chins are like rabbits or guinea pigs, and didn't research proper chin care at all depending on how the chin ended up at the farm.
I don't see anything that shows mistreatment or animal cruelty to report. The living conditions from what I can see unfortunately don't technically qualify as animal cruelty, if no ledges equaled animal cruelty most breeders would be guilty. I know when I first got chins when I was a kid I was told a rabbit cage was an acceptable cage. It looks like it has a house, as well as some kind of steps to jump and play on. I don't know about the UK but most places the only requirements for chins is a cage that is at least about 8 cubic feet of space, with food, water, and shelter. I'm unsure of the temp there, but so long as it is below 25C the chin is no real danger due to lack of AC though, unless it's also very humid there. Also I can't see if it's protected from rain, wind, direct sunlight or not.
If the chin is not being sheltered from the elements, it's hot and humid causing the chin to grow mold or fungus, and they refuse to listen to how to properly care for chins, then yes I could see reporting them. I would talk to them first though, maybe even direct them to this forum to help them learn, or print up a care sheet to show and give to them.