No opportunities for "promotion" yet but have moved between streams quite easily (PM to ENG) and this resulted in a pay rise
Promotion opportunities are quite rigid. You must progress to the next P level by meeting certain requirements. This is a benefit in some ways as it means you know exactly what to do to move up. However, it can be difficult to tick off some of these points as often you are locked in to your project and it might not be at a stage where you can obtain this experience. For example, you might be missing 'requirements writing' and your project is passed that stage.
As an engineer, you can stay in a technical role and work up to subject matter expert or chief engineer etc. or you can move into a management role such as engineering manager or technical director.