That unfortunately is one of the problems of towing on a motorway. If you're not carrying enough speed (in a straight line) to overtake then you all end up running one behind another and the slowest is always at the front !
I seriously doubt a recent 4x4 would slow down to 35mph if he had nothing in front, i.e. there is a reason for him being so slow.
Problem is once you're at that speed its difficult to get on the outside lane and accelerate again (takes ages) as you've just experienced with a 1.8litre petrol engine. You had to stay behind because of traffic etc and could only pull out when safe (rare on a busy motorway) and probably would have slowed down many others when you finally got to overtake.
Put some music on and wait until you get to the track to drive fast.
Other people also have the right to tow their toys and houses around.
As already said, towing is nothing like driving a normal car, and best home safe than with a caravan stuffed up the back of your car.