Took me a moment to understand because I forgot that in the UK the sides are exchanged. Left = Right and Right = Left in traffic. :-)

It is the same in Germany. I always assumed it was that way everywhere.

So if there is a slow car there, what do you do? Does everyone wait behind them until they turn/exit or decide to switch lanes?

If there's a slow car in the outside lane, and they're not making any attempt to overtake anything, you generally flash them until they move over. They are, after all, breaking the law.

What if a car is in the passing lane doing the speed limit? Asking them to move out of the lane so another driver could pass by speeding, breaking the law, doesn't make much sense either.

It's a grey area, although usually accepted that 90% of drivers drive faster than the speed limit anyway.

If it's a 70 limit, and someone is in the passing lane doing 70, you'd still flash them.

Speed limit on an Autobahn?

(OK, there are speed limits on most patches of the Autobahn. But there are some without.)

If he's driving at the same rate as the cars in the inner lane, he shouldn't be in the passing lane.

Yes. It's amazing to watch if you're used to driving in the US. You'll get an unbelievable amount of grief if you allow yourself to be approached from behind in the inside lane. Even driving in the center lane, you are expected to move outside if there is room to do so. Try driving there long-term and you'll get fast drivers cutting you off from the passing lane just to teach you a lesson.

And no, nobody passes on the outside. Even if you're about to exit and the rest of the lanes are moving slowly, you'll still slow down considerably and look a bit sheepish as you drift past the main highway traffic.

Occasionally idiots pass on the outside.