Your car was keyed and repaired costing you £300 and then done again. Do I take it they have only put their hands up for the second 'offence'?
In which case that extra cash your repairer has for you will help offset that first cost, but what troubles me is that he was drunk and keyed twice????? What happens the next time?
In which case if you haven't reported the incidents, and outcome, to the police I would be doing so for the record and as advised ^^^ do keep that original written admission of guilt. You can always say that as you have the admission but been recompensed you are not seeking prosecution but this guy could well do it again (if being drunk was the genuine reason) and if not your car some other poor bugger.
My guess it was the letting agent that put the pressure on and wife saw the writing on the wall...........