London mayor Sadiq Khan has ordered an investigation into the rising bill for converting the London Stadium for use by West Ham amid concerns that taxpayers will be saddled with the costs for years to come.
The Premier League club moved to the centrepiece of the London Olympics this season but it has not been a smooth transition with several incidents of crowd trouble and complaints about a lack of atmosphere.
But Khan, who replaced Boris Johnson as mayor in May, is more concerned about a £51million hike in the cost of transforming the stadium from its Olympic configuration into a 60,000-seat multi-purpose venue fit for top-flight football.
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.
"The former mayor announced just last year that the total cost for transforming the stadium was £272m. In reality this is £323m - a difference of more than £50m.
"Sadiq has ordered a detailed investigation into the full range of financial issues surrounding the stadium.
"We remain committed to the future of the stadium as a venue for football and other sporting and cultural activities, and we are confident that London will host a fantastic World Athletics and Para Athletics Championships in 2017."
When asked for reaction, West Ham chose not to comment.
The club have a 99-year lease on the venue and pay an annual rent of £2.5m, which covers nearly all their costs. They also contributed £15m towards the conversion costs, with the public purse paying the rest.
This has led to widespread criticism from politicians, supporters of other clubs and campaigners for accountable and transparent government.
In a statement sent to Press Association Sport, the chief executive of the TaxPayers' Alliance John O'Connell said: "For too long the details of this shabby deal were kept in secret and lacked proper scrutiny so Sadiq Khan is absolutely right to look again at the case.
"But instead of focusing our anger on West Ham for taking advantage of this ludicrously generous taxpayer-funded subsidy, we should instead be demanding explanations from those that signed off on this agreement and ask how they ever thought that this offered value to those of us footing the bill.
"It's now down the those in charge of the inquiry to get to the bottom of how West Ham were gifted the deal of the century while ensuring their investigation doesn't end up costing the taxpayer as much as the stadium."
Khan's investigation will cover all stadium costs but it is the retractable seating system that was installed to get football fans closer to the pitch that is causing the most alarm.
It is understood that the seats are not as "retractable" as the Greater London Authority, the Stratford venue's owner, had been led to believe and they actually take 15 days to remove or replace.
This means extra costs and delays - a major concern when the stadium's business plan depends on concerts and other events during the football off-season. Depeche Mode are scheduled to play a concert on June 3, three weeks after the football season.
And Sky News has reported that West Ham could be forced to play on the road for the first month of next season.
The GLA says the "final comparable cost" for converting the stadium is now £309m with a further £14m set aside for "essential enhancements". That produces a conversion bill of £323m and final cost for the stadium of £752m.
The original estimate for moving the retractable seating was £300,000 but that is now believed to be wildly optimistic. A tendering process is currently under way for a contractor to do the job going forward, with Sky News suggesting this could cost £8m.
London Assembly member Andrew Dismore said: "This is a staggering burden to place on taxpayers. It's only a year ago that Boris Johnson promised both full transparency and that no more public money would be spent on this project.
"Londoners must now add the stupendous costs of retracting the seating to the other numerous poor deals for the taxpayer the West Ham contract contains.
"Boris even went so far as boasting about the rental income from West Ham, which at £2.5m per season can now be seen to be a drop in the ocean when compared with the cost of retracting the seats.
"Londoners will rightly want to know how they ended up bearing the costs of the former mayor's disastrous negotiations."