The cost of building — and later removing — the now notorious Marble Arch Mound has nearly doubled from the original £3.3 million to £6 million.

As a result, Westminster Council’s deputy leader, Melvyn Caplan, who led the Mound project has resigned, while the council has launched a review into how the project went so badly wrong.

The mound was supposed to cost £2 million to design, build and remove — plus £0.5 million for permanent improvements in the area, but those costs have now jumped to £5.2 million.

Some of the cost rises are apparent in a council document, such as the need to provide full access to Thames Water mains pipe running through the site, road closures to facilitate laydown construction area to the west of the mound and the incorporation of Horse’s Head sculpture into the structure.

The operating costs, such as staffing, have not changed, and remain at £0.8 million.

The original plans had anticipated that the £3.3 million costs would be partially recovered from around £2.1 million in sales, such as ticketing, sponsorships, a cafe and merchandise sales. The cafe still hasn’t arrived, the exhibition isn’t ready yet, and sponsors are running away from the project faster than an Olympic athlete

The council, having admitted that they opened the Mound before the planting had grown properly as they still hope it will, are now offering free tickets for the rest of August – which you can book here.

When the mound is taken down next January, the plan is for the grass to be reused on green roofs and the trees replanted along Oxford Street.