Re: What register?
You can postpone jury service when called to serve if your circumstances would be adversely affected by it. You can only do this once though (as far as i am aware), but in the case of working as a contractor, you should be able to show significant hardship would ensue from loss of income
And the comment saying you can be fined is now correct thanks to a change in the law that nobody cared about or said anything to stop making it a criminal offence not to be registered & for no payment of the fine to be a civil offence with a sliding scale of fees for non-compliance