Sadiq Khan has voiced his upset after the findings of an inquiry into the London Stadium’s finances were delayed by four months.

The mayor of London’s office has ordered representatives from accountancy firm Moore Stephens LLP to attend City Hall tomorrow to explain the hold up with its report.

The meeting will enable Mr Khan’s “frustration and displeasure” over the “repeated delays” to be directly heard, his chief of staff David Bellamy told the London Assembly’s budget monitoring sub-committee yesterday.

Moore Stephens is examining why the costs of converting the former Olympic stadium into the West Ham United arena rose by £51 million from £272m to £323m in 2016.

The company should have completed its three-month independent investigation, ordered by Mr Khan in November 2016, in June.

David Bellamy, from Greater London Authority (GLA), said the firm had experienced “challenges” in securing some of the historical documents needed to complete its £150,000 review “but equally the repeated delays here are just not acceptable”.

He said the realistic publication date would be another few weeks away.

It is believed that the price of retractable seating, used to accommodate football matches and music concerts, is the key factor behind the cost hike.

Gareth Bacon, chair of the budget monitoring sub-committee, said: “One of the things that is a concern is that this report may lead to findings and conclusions that have an impact on the mayor’s budget proposals for next year.”

The committee, which scrutinises money spent by the GLA, also quizzed bosses of the London Legacy Development Corporation (LLDC) about what they were doing to reduce costs.

LLDC chief executive David Goldstone said “corrective steps” had begun, including an engineering study to make the stadium’s seating more efficient.

Better crowd management at Stratford Station was also being introduced “that will reduce stewarding costs significantly”.

However, he added that finding a sponsor for the naming rights of the stadium had been put on hold on until some of the venue’s issues had been resolved so a “clearer proposition could be ready”.

The next committee meeting is scheduled for mid December.

Moore Stephens has been contacted for comment.