Councillors have called for an independent review of a “culture of complacency” at a flagship Tory-run council that ran up a £3m overspend on a much-derided new visitor attraction in London’s West End labelled “Teletubby hill”. An internal Westminster council report, discussed at a council scrutiny meeting on Wednesday evening, admitted the Marble Arch Mound had been badly mismanaged by officials – with unacceptable errors of judgment caused by the desire to rush it through at speed. There were “devastating” failures in the management of the project, the report concluded, including corner-cutting and cover-ups by officials desperate to keep massive overspends and design problems hidden from councillors, and a lack of overall “grip and oversight”. Labour’s opposition group said the report did not go far enough in scrutinising the role of senior elected council leaders, who it said missed several opportunities to challenge and track the progress of the controversial scheme, which it said showed a culture of complacency in the council and a lack of political leadership. “It’s evidence of a Conservative administration on Westminster council that has been in power for far too long. They have become arrogant, out of touch and incompetent and it’s time for a change,” said the Labour group leader, Adam Hug. The mound – a 25-metre high artificial hill built on the corner of Oxford Street and Hyde Park with views across the city – became a laughing stock soon after opening in July. The Daily Telegraph referred to it as a “rather silly hillock” while the New York Times called it “a pile of scaffolding”. Within weeks, a project intended to help reinvigorate the area’s battered retail and hospitality economy had also become a political disaster: the then deputy leader, Melvyn Caplan, resigned after it emerged the original £3m cost had spiralled to £6m, and it came under fire from residents and political opponents. Hug said oral evidence heard at the scrutiny meeting showed Westminster’s political leaders had failed in their responsibility to ask key questions and challenge “optimistic assumptions” about the scheme over a period of several months, despite insisting on big cost reductions early on. The council said the review found no evidence the problems associated with the mound “have occurred or are occurring” elsewhere in the council. Westminster managed projects worth hundreds of millions of pounds a year, it said, and had an “excellent record of delivering to a high standard and within the agreed budget”. The leader of the council, Rachael Robathan, and Caplan – who remains a councillor – were formally requested to give evidence to the meeting, but neither attended and questions were fielded by council officers. The council has previously rejected calls for an independent investigation. Hug said: “We continue to believe the council should undertake an independent review of the failings of the council’s political culture and leadership as evidenced by the mistakes made with the £6m Marble Arch Mound.” The mound was originally intended to recoup £2m of its costs through the sale of visitor tickets priced between £4 and £8, but access was made free in August. The attraction remains open until 9 January next year.