I was in Stalybridge yesterday taking some pictures for the Geograph website.
Having posted this picture of canalside plants, I thought I'd ask on their forum for some help identifying the flowers.
Rosebay willow herb, foxglove, iris, purple loosestrife, monbretia and bullrushes were all mentioned.
To aid identification, I've posted here crops from the original photograph (click on the images to see them full-size)
Someone asked if it was the same clump of flowers as the one in this earlier photograph (shown below) from July 2004.
It is indeed, so below is a crop from the original of that photograph.
Thanks to all the botanists who have a greater knowledge of these things than myself.