Looks like a wild perenial to me mate, snapdragon or simular.
Now as far as the mares tale goes, not bloody easy mate, i burn it myself and cover with plastic sheets.
It is thought to have survived from the dinosaur times, i think the Romans brought it over to plant on the railway lines.
Some weed killers will have a go at it but because of its waxy exterior not good enough, unless you crush the plant first.
I dont think you relly ever get rid of it, more like keep it under control TBH, it doesnt take much from the ground though.