The mayor of London has ordered an independent inquiry into the soaring conversion costs for the former Olympic Stadium that is now home to West Ham United, after it emerged the bill had risen by another £51m to £323m.

The Labour mayor Sadiq Khan, elected to succeed his Conservative predecessor Boris Johnson in May this year, claimed that the finances of the London Stadium had been left in a “total and utter mess by the previous administration” as the cost of the conversion ballooned.

The increase, partly accounted for by increased costs involved in moving the retractable seats installed to convert the stadium into “football mode”, takes the overall cost of the stadium to £752m.

West Ham, the anchor tenants in the stadium during the winter because of a controversial deal in which they pay a basic £2.5m a year in rent, contributed £15m towards the overall conversion costs with the rest largely borne by the taxpayer.

The cost of the conversion of the stadium to retrofit the largest cantilevered roof of its kind and 21,000 retractable seats was originally slated at £154m when West Ham signed a tenancy deal following a protracted and tortuous tender process. That then rose to £193m due to complications with the roof and was finally set at £272m last year. The overall conversion cost is now likely to be £323m, with newfound issues concerning the retractable seats part of the reason for the rise.

The cost of the seats has risen from £300,000 to as much as £8m, while it is understood that plans for the hi-tech digital screen and “wrap” that will surround the stadium have also increased the final bill.

“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,” a spokesman for Khan said.

“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.”

The cost of installing new seats at the London Stadium has risen towards £8m. Photograph: Nick Potts/PA

The latest rise in costs comes at a delicate time when the finances and operation of the London Stadium are under renewed scrutiny. Significant teething troubles surrounding West Ham’s move into the stadium came to a head last week when there was widespread focus on crowd trouble at their EFL Cup tie with Chelsea.

The future of the stadium has been controversial since well before the 2012 Olympic Games. Determined to retain the athletics track as promised, ministers and officials originally left any decision on the stadium’s future hanging in order to proceed with construction.

When Johnson was elected in 2008 he abandoned plans to reduce the capacity to 25,000 and resolved to find a solution involving a top-flight football club that could support a larger stadium.

West Ham won a bitterly fought battle with Spurs, who wanted to knock the stadium down and rebuild it for football, only for the process to collapse under legal challenge. Instead, West Ham were awarded a 99-year tenancy agreement under terms that also allow athletics, concerts and other sports to coexist in the stadium.

Under the terms of the deal, only revealed following a lengthy freedom of information fight by campaigners, the costs of operating the stadium are met by the special purpose vehicle owned by the London Legacy Development Corporation and Newham Council. In turn, it subcontracted the operation of the stadium to the French company Vinci.

Newham Council, which invested a £40m loan for a stake in the E20 Stadium Partnership, said that the independent review would also report jointly to the council.

“I fully support the mayor of London’s call for an independent review into the cost overruns of the London Stadium’s transformation works. It is clear the transformation costs are considerably higher than previously reported and we have a duty to taxpayers to scrutinise this,” said the Newham mayor, Sir Robin Wales. “As co-owners of the stadium, the review will report back to Newham Council and the GLA.”

Both Newham Council and Khan’s office said that they believed the stadium would ultimately succeed as a multi-sport venue. “We remain committed to the future of the stadium as a venue for football and other sporting and cultural activities,” said the spokesman for Khan. “We are confident that London will host a fantastic World Athletics and Para Athletics Championships in 2017.”

The new inquiry was welcomed by campaigners. John O’Connell, chief executive of the TaxPayers’ Alliance, 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.”