Just had a thought! If I got a length of plastic hose pipe, long enough to pass through this tree, cut a slit in its full length and slid it over the phone line in the appropriate position, would this fall foul of BT regulations?
Seems like a reasonable idea, though something more purpose made is available to openreach.
I wouldn't recommended having the NTE located outside the building. This would incur an installation charge for non served premises, so could be expensive and would not be worthwhile IMO.