PLant help please??

PLant help please??

Observation - PLant help please?? - UK and Ireland. Description: This one foxed me though I feel I'm missing something obvious and am going to kick myself. PLant over 1m tall. Similar in habit and general appearance to Himalayan balsam, though obviously flowers very different. Can someone put me out of my misery?!

This one foxed me though I feel I'm missing something obvious and am going to kick myself. PLant over 1m tall. Similar in habit and general appearance to Himalayan balsam, though obviously flowers very different. Can someone put me out of my misery?!