For me, it is always the Rover P6. And not for any design or automotive reason. In the BBC TV series adaptation of John Le Carre's book Tinker, Tailor, Soldier, Spy, the main character, George Smiley, drove a P6. Which ever producer matched this car to this character they did an excellent job. Both are understated, able to blend into the background, quintessentially British, seemingly docile, yet agile and quick when required.