Sadiq Khan, the Mayor of London, has ordered an investigation into a £50m increase in the cost of converting West Ham United's London Stadium.
Boris Johnson, Khan's predecessor, had said in 2015 that the change from an Olympic arena to a football stadium would cost £272m.
According to Sky News, that figure has now risen to £323m, with the estimated annual cost of moving "retractable" seats, installed to improve the view for football, reportedly increasing to £8m.
A spokesperson for Khan said: "The mayor is deeply concerned about the finances of the Olympic Stadium, which have clearly been left in a total and utter mess by the previous administration at City Hall.
"Sadiq has ordered a detailed investigation into the full range of financial issues surrounding the stadium."
The Hammers won the bid to occupy the Olympic Stadium in March 2013 and played their first game there in August 2016.
