Why screen any privately operated aircraft?
Today, no privately operated aircraft needs screening, which is rational and logical.
Neither the owner of an aircraft, his friends, family or customers are likely to either blow themselves up or hijack the aircraft - the owner/operator of the aircraft knows exactly who is allowed/invited on the aircraft - no strangers or unknown characters will/can board a privately owned/operated aircraft.
Consistent with today's policies, there simply is no point in screening for private ops. The aircraft size is wholly irrelevant as the risk of any person boarding the aircraft with malintent is extraordinary small.
As for charter ops or any ops for hire and reward, or pay per seat, rather than the 10 tonnes/20 pax and above ruling, why not tie in for simplicity's sake with the catorgarisation for fire and rescue services - i.e. aircraft size rather than weight. A close match for the current criteria would be CAT 4 RFF aircraft or above, when used for public transport purposes, should be screened, anything private of any weight doesn't and CAT 3 RFF aircraft and below don't need screening.
If anyone wanted to cause major horror, public unrest, fear and disruption, surely the easiest thing in the world is to drive a Transit van loaded with whatever one chose to use and bowing it up near any major mode of ground transport, notable public building or in the basement of a significant tower. Or severl Transit vans blown up at sevral locations at the same time.
Hijiacking a private aircraft with intent to commit suicide and cause harm to others on the ground is virtually impossible and has never actually been undertaken. Aircraft owners prefer not to welcome terrorists on board their pride and joy as a matter of course!
Any requirement to screen private aircraft will be a whollly pointless exercise and cause critical damage to a business aviation industry already struggling to survive. I have no doubt whatsoever that certain owners of aircraft who have to be subjected to any screening process will just give up on business avaition and admit defeat.
How exactly are any smaller airfields in the UK be able to comply? They won't and so will suffer considerably. If the DfT try to differentiate between small airfields and larger ones and one set of rules for some and others for lesser ports - that too will be wholly unacceptable. It's all airfields comply under exactly the same terms, or the rules stay as they are and we retain a GA industry and get on with our business with an exceptional record of control and dilligent care taken by crews and operators as to what's going on with their aircraft.