Councillors have demanded an independent investigation into a "culture of complacency" at a Tory-run authority that overspent £3 million on a much-maligned new tourist attraction in London's West End dubbed "Teletubby Hill."

The Marble Arch Mound has been severely administered by authorities, according to an internal Westminster council study reviewed at a council scrutiny meeting on Wednesday evening.

The audit determined that there were "devastating" failings in the project's administration, including "cutting corners" and "covering up" by officials anxious to keep enormous overspends and architectural flaws secret from councillors, as well as a lack of general "grip and oversight."

The report, according to Labour's opposition group, did not go far enough in scrutinizing the role of senior elected council leaders, who it claimed missed several opportunities to challenge and track the controversial scheme's progress, demonstrating a culture of complacency and a lack of political leadership in the council.

"It's evidence of a Westminster council Conservative administration that has been in power for far too long." They've grown arrogant, out of touch, and inept, and it's time for a change," said Adam Hug, the Labour Party's group leader.

The mound, a 25-meter-high artificial hill with views of the city created on the junction of Oxford Street and Hyde Park in July, quickly became a laughingstock. It was described as a "rather silly hillock" by the Daily Telegraph, and as "a pile of scaffolding" by the New York Times.

Within weeks, a project intended to help the area's battered retail and hospitality economy had also turned into a political disaster: Melvyn Caplan, the deputy leader at the time, resigned after it was revealed that the project's original £3 million cost had ballooned to £6 million, drawing criticism from residents and political opponents.

Hug said that oral testimony heard at the scrutiny meeting revealed Westminster's political leaders had neglected to raise vital questions and confront "optimistic assumptions" about the programme over a period of months, despite pushing on significant cost cuts early on.

The study found no indication that the issues related with the mound "have occurred or are occurring" anywhere in the municipality, according to the council.

Westminster was in charge of projects worth hundreds of millions of pounds each year and had a "excellent track record of delivering to a high standard and within the agreed budget," according to the report.

The meeting's leader, Rachael Robathan, and Caplan – who is still a councillor – were both officially summoned to give evidence, but neither showed up, and questions were answered by council staff. Calls for an independent probe have already been denied by the council.

"We continue to believe the council should conduct an independent review of the council's political culture and leadership, as evidenced by the £6 million Marble Arch Mound mistakes," Hug added.

The mound was supposed to repay £2 million in expenditures by selling tourist tickets ranging from £4 to £8, but in August, entrance was turned free. The attraction will be open until January 9th of the following year.

Thanks to Patrick Butler at The Guardian whose reporting provided the original basis for this story.