So turns out that those magic erasers you can get from Wilkos are too strong for wall paint.
On a brighter note, this didn't happen on a big wall like that, so I'm not gonna have to paint an entire side of my flat, it happened around a window, so I can get away with just using a tester pot to repaint the area around the windowsill.
On a brighter note, this didn't happen on a big wall like that, so I'm not gonna have to paint an entire side of my flat, it happened around a window, so I can get away with just using a tester pot to repaint the area around the windowsill.