A Conservative councillor who spearheaded the building of a 25-metre artificial hill intended to tempt shoppers back to central London has resigned after costs nearly doubled to £6m. The Marble Arch Mound has faced widespread criticism and mockery since it appeared on the corner of Hyde Park and Oxford Street in July. The cost of the project had first been reported as £2m, but on Friday it emerged that was only the build cost. The actual forecast had been £3.3m and it was now an estimated £6m. Westminster council’s deputy leader, Melvyn Caplan, resigned with immediate effect, the council said. Visitors were being charged between £4.50 and £8 to climb the architect-designed mound but “teething problems” forced the council to offer refunds. It will remain free to enter during August. In a statement, the council leader, Rachael Robathan, said: “The mound opened too early, and we have apologised for that. It has become clear that costs have risen more than anticipated and that is totally unacceptable. “Total costs are now £6m, covering every aspect of the project: construction, operation and eventual removal. With regret, I have accepted the resignation of my deputy leader, Melvyn Caplan, who led the mound project. We have also instigated a thorough internal review to understand what went wrong and ensure it never happens again.” Robathan defended the motivation for the mound, which, she said, was a small part of the council’s wider £150m investment in the Oxford Street district. “Central London has a battle on its hands,” she said. “Having suffered 18 months of the pandemic, we have to get people back into the city.” Even with the removal of Covid restrictions, the council estimates that footfall in Westminster is about 50% down on pre-pandemic levels. Nearly a fifth of shops on Oxford Street have closed permanently as a result of the pandemic. The project, Robathan said, was one part of an aspiration to help “bring the buzz and footfall back” and “doing nothing was never an option”. The mound was designed by Rotterdam-based architects MVRDV, a firm that claims to create “happy and adventurous places”. It was intended as a novelty experience – in the spirit of New York’s High Line – offering views over Hyde Park and central London streets. Winy Maas, the founding partner of MVRDV, told the Guardian that they originally wanted the hill to totally cover Marble Arch. Conservation experts warned that could cause serious damage and the potential collapse of the arch. Critical reaction to the mound was lukewarm. The Guardian’s Oliver Wainwright said it did not live up to the CGI plans depicting “a lush landscape of thick vegetation, dotted with mature trees, the reality is thin sedum matting clinging desperately to the sheer walls of the structure, punctuated by occasional spindly trees. The recent heatwave hasn’t helped, but none of the greenery looks happy”. The mound was also mocked on social media, with some comparing it to the set of Teletubbies; others to the blocky landscapes seen on the videogame Super Mario 64. Robathan said it was fine to have different opinions on a structure that will remain in place until January. “When the mound fully reopens in September, I hope that people will come and see it for themselves,” she said. “The mound may delight or divide views and that’s OK, but we’re confident that in the end it will fulfil its original brief – to get people back into the West End and remind them of why this is a world-class city.”