Ground/foundation movement

True story. An old friend of my parents went after a beautiful house overlooking the river stour in constable country. On the side of a hill, it was far cheaper than it should have been because it had a good few cracks and the surveys came through that it needed substantial underpinning. They bought it at a big discount, planning to do the work.

My stepfather was a horticulturist and arborist. The plot was bordered on two sides with rows of tall poplars. He said cut them down (you could then - this was 1980's) and the problem will go away. They cut them down, and the land lifted, and the house has been fine since then without the foundations ever being touched.

As @^woody^ says, you need to find out why it cracked in the first place...

Putting a beam in would just concentrate the load onto two neighbouring points, possibly making them move where they were previously stable.

It's all too complicated for a bunch of people who've never seen it to comment.

My instinct is always that if it's broken then it needs replacing, not patching up and pratting about with. My assumption is that it wasn't deep enough, you need to dig down beyond whatever rubbish it was sitting on. But I don't know, as I'm not there and nobody's yet dug down to have a look by the sound of it so everyone's typing words and disclaimers into computers instead of actually doing anything useful.

Yes it is difficult without seeing it., I have arranged to get further advice. I've now exposed the foundation, I could go further but I have a neighbour on one side and there's legal issues with going below foundation level.
In terms of possible causes of ground movement on old properties, It can only really be water can't it ? I've no trees nearby and any natural settlement surely would have occurred long ago, I would have thought.