At 3000ft were cleared for the approach so once you're established on that approach you may descend with it.
Nope, you're not established on a published segment of the approach.
"The final approach segment begins at the final approach point (FAP). This is a point in space on the final approach track where the intermediate approach altitude/height intercepts the nominal glide path".
You're two miles further out than the FAP, and therefore not on the published final approach segment.
Of course, every pilot would descend on the glide, and every ATCO would ensure that such a descent was terrain-safe -- not difficult in this case, but it could create an issue at the extremity of coverage. I'm just pointing out that there are occasions when there is an implicit instruction to descend -- and spud3's case is arguably one of them.