Impatiens Glandulifera

Out for a bike ride today, I noticed that the Himalayan Balsam which plagues us round here is back with a vengeance this year and has just flowered.
They are quite pretty, but are also extremely invasive and a menace. Lots of them can be found alongside rivers and canals. They are related to the 'Busy Lizzie' but grow to 6 feet or more and spread quickly smothering other vegetation. As its name suggests it is native to the Himalayas.
There are various groups organising "Balsam bashing" sessions across the UK in an effort to control the spread of this plant, although the problem remains.