When we were developing 12Pay we hadn't yet registered the company as an employer, and we wanted sample P45, P60 documents etc (not images on the internet, but actual paper copies are needed for print design because registration may vary by a mm or 2 compared with PDF prints), but HMRC couldn't send us any because we didn't have an employer reference. They literally have no mechanism for sending these documents out except to registered employers, so we had to register as an employer to get them.