Finally sorted it!
Turned out the brushes in the motor after 12 years had finally worn out, the remaining fragment from one of the three brushes had then jammed against one of the rotor contacts breaking it loose and making it unservicable. £40 later on a second hand motor got it working again.
The whole unit is not as well designed as I hoped and does not make it easy to remove and replace the motor, I should also add that there are infact 2 motors, one to run the wipers and the other to park them.
Removing the motor from the unit requires a hammer and removing the wiper blades and arms from the unit require some elbow grease if they have been put on tight.
For all those looking to attempt this:
Remove wiper blades and then arms.
Remove plastic trim from both sides.
Undo 4 bolts holding unit in place, making sure to remember that 1 out of the 4 has a round sleeve and not an oval one.
Remove cable ties.
Use a socket/spanner to rotate motor assembly bolt to give access to the 3 screws holding motor in place. Dont undo screws yet.
Undo that bolt.
Undo the 3 screws.
Use hammer to seperate motor assembly from arm.
When putting it all back together, remember to turn the wipers on and then off prior to reattaching the wipers or the arms so that the motor goes back to the parked position.
Install the wipers in the parked position.
And I believe thats it!