There are not many places where you can run into a traffic jam in London at 3.45am, but the roundabout at Blackwall, north of Canary Wharf, is gridlock. Lots of vans. All heading into Billingsgate Fish Market, which has been at its current location since 1982 after being located from its original location at Billingsgate, where fish had been traded since the 16th century.
It's quite a sight, with fish and seafood of all descriptions piled up as buyers hand over cash and receive bags and boxes in return. Porters trundle up and down the aisles with big trolleys piled high with boxes. It smells very fishy, as you would imagine.
Restaurants come to buy their fish, but there are lots of private buyers too: lots of Chinese and Italians, with many snapping photos of fish on their phones and sending off to people (perhaps knowledgeable mothers) to ask for second opinions on whether they should be purchased.
The market is soon to be moved even further east out of the city: the plot of land the market currently sits on lies literally in the shadow of the towers of Canary Wharf, and is no doubt worth more to the City of London as residential land than a fish market.