If you do not register, you will not be able to be appointed to matches by any competition affiliated to the FA or the County FA. You would not be covered by the County’s Public Liability Insurance and there would be no chance of receiving County Cup Final or Representative Match appointments.
There would also be no opportunity for promotion, no communications from your County FA (newsletters and invitations to training and other events), you would not receive any information on updates/amendments to the Laws of the Game annually and you would not receive a County handbook. Your details will not appear in the County handbook.
After two years of being unregistered, you would have to take the exams again if you wanted to re-register and after five years you would have to take the whole course again.
As an unregistered referee, you would only be able to referee as a 'club referee' and be appointed to games by a home club if no registered referee is appointed by a competition. Naturally, this would limit where you could referee and the level of game you would be offered.