tin hat on
Regarding the vandalism. If it is indeed such a widespread problem. Then the aircraft should be checked before departure from LHR as being 'clean'. On arrival at the destination they should be rechecked, prior to crew disembarkation, by the station manager (or duty officer/ground engineer). If any vandalism is found then suspend the crew (individual or multiple) subject to displinary action. Simple, make an example of a few and it will soon stop.