The idea was Iain’s, noticing that I rarely ventured south of the river he suggested a walk through his manor, Beckenham, following the River Beck. In the course of deciding where to start we somehow settled on the mouth of the River Ravensbourne at Deptford Creek.

We worked our way South through morning Greenwich and over Deptford Bridge, through Brookmill Park to Lewisham, where we gave a nod to the River Quaggy. The passage through Ladywell took me back to the walk I did for This Other London in autumn 2012 to Herne Hill Velodrome that passed this way over Ladywell Fields. Where I peeled off that day over Blythe Hill, Iain and I carried on beside the waters of the Ravensbourne across Catford Bridge to the Linear Park where the Ravensbourne departs and we followed the Pool River to Bellingham.

In Cator Park, Beckenham (after a David Bowie detour) we find the confluence of the Pool and the Beck (and also see the Chaffinch Brook) and from this point, entering early evening and pushing on for 15 miles for the day, we are now fixed on the source of The Beck.

Families are out in force perambulating around the broad waters of Kelsey Park, it’s a good time to stop for ice cream. It gives us the legs to push on through outer suburbia bound for Shirley.

I won’t spoil the end of the video, but the moment of finding the source, not quite where we expected, was a moment of mild euphoria. 21-miles river walking through South London, two middle-aged men gazed with love and amazement at a trickle of water dribbling from a pipe in a narrow strip of woodland in Shirley.