Could be that the aircraft was originally looking to land at Biggin Hill, but then there was a change of plan and they were heading off to some place else instead…that’s the joy and luxury of travelling in a private jet, you can simply do these things!?

Not that easy… There’s things like flight plans need filing to operate IFR etc. and it’s fairly unlikely London would accept one over the radio especially at busy times. Unlikely it was a divert away from Biggin as the weather was good and I suspect any alternate would not need them to climb to 20000 again.

More likely i think the a/c had some sort of problem and was diverting to Biggin, and then they got the problem sorted before they landed and they decided tiresome their original plan.

Andy