You can cut back by sawing the trunk through at an angle to allow rain to run off, but I definitely don't recommend you do this now - it will have to wait until late April, when the weather has warmed somewhat and the growing season has begun, otherwise you risk losing it during this winter.

Hi, welcome to GoY, just out of curiosity, how do you mean to manage it, it doesn't need any pruning, and any dead leaves will fall off of their own accord, although it may look a bit untidy, there's no need to take them off, so I'm wondering what you mean by 'unmanageable' Derek.

I'm guessing Amchurchill means they don't want it that tall, and certainly not any taller, Derekm...

Its meant to be a tree when its mature after all...