AIUI in that situation it's still all the same rules and repayments but HMRC no longer have access to your tax code or income, so you have to provide evidence.
If you disappear your rate is charged the maximum monthly amount and you are charged interest on late payments.
I do my dept head's house alarm (can't remember him)
I used to do my primary school teachers house alarm, IIRC in the class was 6 lads sat in the table in the middle 5 of 'em called Dave