In 2013, a year after discovering the regular Sand Martin's breeding site (by Leyton Marsh), I took these photos.
I'm pleased to say that for the last four years of my watching the site, they're back in strength.
I spent a pleasant 30 minutes observing them dash around at their usual spot.
There were two Yellow Wagtail on the rear paddocks.
Then I was treated to an aerial display of all three British hirundines - House Martins, Sand Martins and Swallows. They were feeding over the flood relief channel. The House Martins were also swooping over the rear paddocks, picking up mud to reinforce their established nests in the nearby Coppermill Treatment Works.