From the City of London, via the Thames Conservancy, the PLA inherited the conservancy, management and control of the river instead of ownership of the bed of the river and foreshore (the Crown was prohibited from alienating any of its lands by section 5 of the Crown Lands Act 1702; the Crown was presumed to own the bed of Thames and 'as conservators' the City of London were prohibited from owning any part of that same river bed) from Teddington to the Yantlet Line (between Southend and Grain).

Today the PLA acts mainly as a managing authority for the tidal stretch of the River Thames, ensuring safe navigation, and the well-being of the port and its activities.

The PLA retains a presence in the City in offices at Pinnacle House on St. Dunstan's Hill, where the Chair and Chief Executive are based.

This included engine sheds, located at Millwall, Tilbury and Custom House, its own signal boxes and level crossings.

The main duties undertaken by the authority's locomotives were shunting the various sidings, wharves and factories around the PLA estate.

[11] The PLA operated a fleet of 0-6-0T and 0-6-0ST steam locomotives made by various manufacturers including Hudswell Clark, Robert Stephenson, Andrew Barclay, Hunslet and Manning Wardle.

The blazon or heraldic description is as follows: Azure, issuing from a castle argent, a demi-man vested, holding in the dexter hand a drawn sword, and in the sinister a scroll Or, the one representing the Tower of London, the other the figure of St Paul, the patron saint of London.Crest: On a wreath of the colours, an ancient ship Or, the main sail charged with the arms of the City of London.

Supporters: On either side a sea-lion argent, crined, finned and tufted or, issuing from waves of the sea proper, that to the sinister grasping the banner of King Edward II; that to the dexter the banner of King Edward VII[15]The Latin motto is "Floreat Imperii Portvs", meaning "May the Port of the Empire Flourish".