The Lambeth North branch of NatWest officially closed in June after a prolonged shutdown during the COVID-19 pandemic.
The Royal Bank of Scotland plc, owners of NatWest, applied to Lambeth Council for permission to fill in the hole where the cash machine used to be located and to make good the frontage of the disused bank.
The works were carried out before the council made a decision on the planning application, and the ATM space was filled in with crude concrete blocks.
Lambeth planners have refused permission for the works, branding them "unacceptable".
The refusal of planning permission says that "by reason of their unsympathetic design and materials and in the absence of planning permission would result in less than substantial harm to the shopfront to the detriment of the locally listed building and the surrounding Lower Marsh Conservation Area"
In their report accompanying the decision, Lambeth planners note that the bank "is an impressive locally listed late Victorian block constructed in 1894".
They add: "The principle of the removal of the ATM is acceptable. However, the works have been undertaken on site without planning permission.
"The works have not been made good to the existing and the infill material that has been erected on site does not appear to match the materials of the host building.
"Furthermore, the removal of the ATM would require the repair and installation of the cornice to the window above."
The former banking hall is currently to let for alternative uses.