Non-retaining wall... Wall

So I have this dirt wall that at its highest is about 2m unretained.

If I was to put in a 2m retaining wall, I'd assume I'd need consent? As it stands I'm also assuming it doesn't need consent as it wasn't mentioned on the builders report ~10 years ago.

Firstly are my assumptions correct? And secondly, if I was to retain up to 1, 1.5M, would I require consent?

And thirdly, taking suggestions for what to do. It's a steep hillside section. It would be nice to level it all and shift the dirt if that could be done, again without the consent ha$$le

Thanks all