Yes, if you're planting it on your property. If you're worried about it proliferating on the railway, dead head the spent flowers.

Yes. Millions of gardens across the UK have buddleia without it spreading everywhere and without it being any problem. Carry on.

Oddly enough it is of the the most common shrubs that you see along the railway embankments so one more from you will not do the nation any harm.

I certainly do not view it as invasive far worse shrubs. One has self seeded in our garden and as it is in an awkward spot am simply going to let be. I will keep it well cut back and the insect life will love it when it flowers. The trick, if there is a trick, is not to let it grow bigger than you want it to, prune hard.

And if you need to you can prune often without killing the plant. You may lose some flowers, that's all.

Exactly

Thankyou to everyone who answered me on my buddleia question,i am very grateful .
cokeyg.