So I figured out the ABS sensor on the rear right wheel was bad and bought a replacement for £50, that solved the first fault code. The second code then came up, "motor overrun". The abs pump motor has failed basically and they are like gold dust.
I've disconnected the ABS ecu and now the ABS is "disabled" rather then "faulty" the four wheel steering works.
Its amazing fun! Especially in a multistory at 10mph, but you can feel the rear end turn in at higher speeds.