Unwanted buddleia

Silly question time - does anyone have any recommendations for dealing with an unwanted buddleia that is growing in a bloomin' awkward spot?

I have one that is having a good go at thriving behind my greenhouse (see photo below), so I can't really get at it - would something like round up hit it hard enough or would I need SBK? Napalm??

 

Good evening @Fat Controller I have three of those in my wildlife garden they attract all the Butterflies are you sure you don't want to keep it

 

It is actually daughter of fallen buddleia tree that was sited about 10-15ft away in the border of the back garden and blew down in a storm. I quite like them, but not a fan of it being where it is

More than anything I am concerned about it either popping greenhouse glass or knackering the fence it is up against.

 

Thankfully there is only a patio behind the fence - my neighbour is fantastic too, so if I needed to get to the roots (under the fence) he would likely let me at it; trouble is, neither he or I have the grunt to remove a fence panel nowadays....

I have some round up in the shed, so will mix some into a pressure sprayer and give it a go I think. Cheers @pete

 

Be really careful with roundup anywhere near tomato plants, they keel over and die at the slightest whiff. I seem to recall you had some in your greenhouse. Even getting a little residue on clothing and entering a greenhouse can be fatal.

 

I do agree you need to get rid of the butterfly bush though it could adversely affect your greenhouse. Maybe take out all your seedlings and keep away from that area whilst you spray?