I am interested if airplanes (of any sort) are ever (perhaps periodically) sent away to a facility for maintenance? I’m thinking somewhere away from the exceptionally high levels of security you would find in an airport. Perhaps somewhere where staff are not subject to the same level of security checks.

That depends. Some airlines do everything in-house, some airlines do everything but the D-check (link) (the most comprehensive checks). Others outsource everything.

One of the airports nearby (Maastricht, NL) has a large maintenance fascility for Bombardier DHC-8s. Planes from all over Europe and North Africa visit here frequently, with visitors from further away dropping in from time to time as well. Luton has a large maintenance fascility for Gulfstream jets, Woensdrecht (NL) a large fascility for Fokkers and Airbusses, Moenchengladbach (DE) has a large fascility for ATRs and so on. The same minimum security standards apply as they do at say Heathrow, Schiphol or Frankfurt. But of you’ll understand that the large hubs go above and beyond minimum requirements as they have vastly more manpower and much larger budgets. Just to be clear, I most definately do NOT want to imply security at minor airports is insufficient!

Perhaps the plane could be modified in some way during ‘maintenance’ and drugs could then be stored for transportation. Is there any way I could make this work?

Sure there is. From time to time you hear the police arresting ramp personnel or maintenance crew. There is a lot of money in drugs trafficing so it should come as no surprise that some people take the offer. Or they can be blackmailed into doing so (Dutch link , please use Google translate). And this is definately not limited to minor airports, it also happens at large airports like Schiphol (link) or Heathrow (link).

Could anyone shed any light on what sort of security checks are made on private jets? I’m not looking for full details on how one might smuggle drugs onto a jet but just some basic info which might give me an idea as to whether I should research this method more.

Same as with the big jets. The passengers and luggage will go through the scanners, but the plane is not normally turned inside-out, though the sniffer dogs can spot check any plane they like. I don’t know about the situation in England, but at Schiphol the Paramaribo flights where notorious for drugs running. A few years ago the police started to check 100% of the passengers and freight and they continue doing so to this day. Despite the 100% checks the police still occaisionally find drugs.