When I took over my allotment a few years ago, there was a rose tree/bush
that I presume started out as a "proper" rose but has since gone wild. The
trouble is that I've never been sure how to prune it.

It's approximately 9 foot high, but the first 3 foot at least is just bare
"trunk". It used to flower, but the last couple of years it hasn't (probably
due to my pruning). What I've done the last couple of years, to try and get
it under control is chop off about half the height of the stems that have
leaves on them, but all that happens is they shoot up within a couple of
months to the same height (if not a little higher) to what I cut off, and
don't even flower now.

What I would really like to know, is can I prune it severely even to where
the trunk part is? Would this promote growth to start lower down. The trunk
is very old looking a gnarly, would it send new shoots out or not? Id prefer
it to be a height of about 6 foot, with less bare trunk and of course to be
flowering again.

Any advice appreciated.