So I got a cloth and wiped it, and the wall moved.
My first reaction was panic as I thought I'd broken the flat already but then I realised it's a fake wall, it hides this
It would be pretty simple, you wouldn't even need any power tools if you got the wood pre cut to size at the shop (Some DIY chains offer this in larger stores), then glue it together and just paint over. Adding backsplash or trim really would make it look realistic but if you can't find the one to match the existing trim in the room or don't want to spend the money it would still look better than a mess of pipes, note in the second to last picture the semicircle cut out of the bottom right of the fake wall though, so it sits over the existing trim and fits snugly to the wall. You could even go the whole hog and get tiles, then it would really blend in to a kitchen or bathroom seamlessly. This is going in a mental file of things to remember when we move, as there's nowhere else in the flat I'd need to do this but I wish I'd thought of it at previous properties.
Have you ever found something weird in a new house?