poplar dock line traction

[shaffers]

As a young lad growing up in poplar we could see the ocasional frieght train as it passed langdon park playground pulling loads of concrete pipe and closed wagons.
can anyone please tell me what type of locomotives were used on the line in the BR days and if these trains were carrying export traffic to the docks or was the line being used as a link to harrow lane for shunting purposes.

thank you to everyone
George AKA shaffers