The tiniest little blip flickered on the Heathrow air traffic control radar. A vigilant controller just spotted it; after the haranguing from security they'd had only that morning on home grown terrorism.
Fighters were dispatched; and the unconventional aircraft was forcibly landed on the tarmac; quickly being surrounded by police vehicles and marksmen.
The reindeer were bundled off to the cat meat factory and Santa headed towards immigration; the sledge impounded.
Two years later and Santa is still in detention, identity unverified, and awaiting deportation – to where? who knows? – they cannot find a country that will have him.