Trump could surprise the British resister hordes if he goes by sea. A carrier could make it in 4 days, chopper to an LPD in the Channel, from which an LCAC could take the Trumpster and his motorcade up the Thames to the landing ramp closest to the US embassy.

If speed is important, a Minotaur rocket (surplus Minuteman ICBM) could be rigged with a small capsule (suitably equipped with reentry shield, parachute, and Big Macs) and launched on a suborbital trajectory that would deposit its pantload; er, payload; right on the embassy grounds in London. I’m sure 5 days is plenty of time to develop such a thing and perform appropriate safety tests.