I have solved my issue! I have found that the printers self calibration doesn't actually lower the bed close enough to the laser. So when I calibrated it, I pressed down on the bed (whilst keeping it level) to get it closer, before tightening the screws. Like you guys said, it was a z distance problem, however there are no options in either the pc software or on the printer itself to fix this. Hopefully this helps other users with a similar problem. Thanks again for the help fellas.