Complex sentence: The docks were finally closed to shipping in 1969 and sold to the borough of Tower Hamlets, which filled in the western portion of the London Docks with the (unrealised) intention of turning them into public housing estates.
Split into simpler sentences: The docks were closed to shipping in 1969 and sold to the borough of Tower Hamlets. The western portion of the London Docks was filled in with the (unrealised) intention of turning them into public housing estates.