Leaders in charge of the troubled attraction hid “critical” information from cabinet members and over estimated how much the mound would make in ticket sales, the council commissioned review said.
Westminster had originally hoped to recoup the majority of costs by charging tourists eager to clamber up the installation at the end of Oxford Street up to £8 a ticket for an adult and £20 for a family of four.
The council had forecast 280,000 paying customers - with sponsorship making up the shortfall. But it forced to drop the fee altogether after the first visitors branded the manmade hillock “London’s worst tourist attraction”.
Westminster council then admitted the cost of building and maintaining the mound had tripled from £2million to £6million.
“In order to meet the cost expectation, set by the responsible cabinet member, the Review Team found evidence that the senior officers responsible for the project descoped and omitted critical elements of the Marble Arch Mound project,” the report stated.
“At the same time income estimates were revised upwards with no evidence provided to support these assumptions.”
It added: “Despite clear and repeated warnings around the likely cost of undertaking such a project from experienced officers and the suppliers tasked with building the Mound, overly optimistic financial updates were given to senior leaders.”
The project was also not scrutised by the council’s Capital Review Group (CRG) which prioritises capital spend and challenges project finances to ensure investments are backed up by a business case.
“The fact that the project was not taken through the CRG process meant circumventing a key check and balance within the council,” the report found.
The town hall had hoped the mound would bring up to 1,000 visitors a day to the West End.
Visitors climb 130 steps to a viewing platform to see views of Edgeware Road, Hyde Park and Oxford Street. A light installation, which opened seven weeks late, is based inside the structure.
Westminster North MP Karen Buck described the attraction as a “£6million catastrophe”, which had cost residents “£150,000 every month while services get ever more squeezed”.
Council chief executive Stuart Love said: “The council must learn the lessons of the mound project.
“We will continue our efforts to revive Westminster’s economy post-pandemic and to ensure our residents continue to receive first class services.”