Not familiar with the London airport situation:
Historically, civilian biz-jet traffic heading for London was 99% LHR, but that was back in the 70's when biz-jets were less common, and at Heathrow you could even find light twins mixing it with the airliner traffic. (see photos)
Military and pseudo-military transports were split between LHR and RAF Northolt. If it was a head-of-state coming on a personal shopping trip for Xmas, they slipped quietly into Northolt. If it was a full state visit, they used Heathrow and made the front page.
Luton had a small biz-jet community of it's own
Gatwick was chosen by very few.
Biggin Hill was strictly GA even though it had a decent runway.
And Stansted wasn't even on the list.
Since then, much has changed.
For a start, the area for biz-jets at Heathrow was demolished many years ago in favor of Terminal 4.
Larger (airliner size) jets would have been parked near the fuel farm, or lost somewhere in the Cargo Center, but neither of those are an option anymore either.
Both Northolt and Biggin Hill have more recently developed dedicated biz-jet facilities that I suspect basically inherited areas of the airfield left vacant as the RAF presence shrunk or vanished completely. Landing charges at these sites are obviously much lower than Heathrow, and there may also be a "feel-good factor" from having the shiniest toy on the apron and being the only VIP in the terminal, as opposed to getting lost in mountains of human traffic at Heathrow.
Luton now has a massive biz-jet community of it's own, and naturally attracts visiting a/c too.
However, none of the three above has either the runway length or ground facilities to handle the biggest jets that some heads of state seem to need these days, hence Stansted has become #1 choice for the really big boys.
Here are some memories of the old Heathrow business aviation area before it was lost under Teminal 4.
Firstly a Cessna 310 together with a PA-23, next the biggest baddest executive toy of that era, the Playboy DC-9 N950PB, and finally… on a really good day, there might be as many as two
And to help with context, some wider shots showing the whole landscape at LHR in the 70's. In the distance, behind the MSA 707, three biz-jets parked up in front of the Pan Am maintenance hangar, and facing the "Field Aviation Services" / "Hunting" hangars adjacent to the old business aviation area. At a wild guess, they are (L to R) N10XY, N655GP, and N228Z
The second photo shows a much wider angle and includes the prominent "Hunting" logo on the back of the hangars that were home to a clutch of British registered HS.125s.
(note the Air France 727 with it's dirty tail; plus ça change, plus c'est la même chose
Nothing to see here; move along please.