[Hybrid tellies]

Reception of uhf tv in a moving car will be a very fluttery affair (on analogue tv) due to the nature of uhf propagation. Because you are moving along at almost ground level the field strength pattern will be continually varying due to reflections and screening effects of buildings, hills, & trees etc. Only in very very favourable locations will you get reasonable results.

As you said, electrical interference from the car ignition system is much less on uhf than on the vhf bands but the propagation disturbances are far worse. As for freeview, the problems won't so much be a fluttering picture, but one of blank screens and at best freezing or severely pixellating pictures.
Unfortunately, the uhf tv system was not designed for mobile use but more for viewers with fixed receivers and aerials. This was the same for vhf radio until they upgraded all the FM stations back in the 1980s to improve reception on portable and car radios.
I would imagine recepton on any tv in the back of a limousine would be the same, even with an external aerial fitted, and I think they are more for people to watch recorded programmes on a vcr or a dvd.