At my last MOT the garage nearly failed my Ford Focus because the tax disc was displayed inside the arc of the windscreen wiper.
I was told to move the sticker to more than 40mm outside the windscreen wiper coverage or the car would fail the MOT. This meant the sticker had to be moved to near the top of the screen kerbside.
Display a tax disc on the passenger side (kerb side) of the vehicle�s windscreen. If there�s no windscreen or you have a motorcycle or sidecar, display the tax disc on the kerb side of the vehicle.