London Mayor Sadiq Khan is to take over control of the London Stadium, after an independent review revealed “a catalogue of errors” leading to massively increased costs during the stadium’s conversion after the London 2012 Olympics.

The review, published yesterday, called the conversion a “bungled decision that has left the taxpayer to foot an annual loss of around £20 million.”

Mr Khan said: “I ordered the review into the finances of the London Stadium to understand how key decisions were made about its transformation and why costs were allowed to spiral out of control.

“What has been presented is simply staggering. Not for the first time, it reveals a bungled decision-making process that has the previous mayor’s fingerprints all over it.”

Mr Khan ordered the investigation after learning that the bill to taxpayers for converting the centrepiece of the London 2012 Olympic and Paralympic Games into a multi-purpose venue had climbed to £323m.

London Legacy Development Corporation (LLDC), the body which operates the stadium for the Greater London Authority, admitted that problems with the venue’s retractable seating were the biggest cause of the rise in costs.

Premier League side West Ham, which have a 99-year lease on the 60,000-seat stadium, made a one-off contribution of £15m to the conversion costs and pay £2.5m a year in rent. The total price tag for the stadium, which also has a new roof, is estimated to be £752m

“Boris Johnson clearly panicked when faced with legal challenges about West Ham and Newham’s joint bid to take ownership of the stadium and then decided to rerun the bid process with the taxpayer taking all the risks and footing almost the whole bill. You simply couldn’t make it up,” Mr Khan said.

“I am determined to put the London Stadium on a stronger financial footing and secure its long-term future, but I’m under no illusion that this is going to take time and some real commitment from all partners to make this work.”

West Ham issued a statement in response to the report saying it will “continue to devote our absolute commitment to London Stadium,” adding that its first priority is “always to act in the best interests of our supporters.”

The statement concluded that “the stadium itself craves renewed leadership and direction and we welcome the mayor’s decision to step in and deliver this. West Ham United is firmly behind him.”