The man in charge of the Olympic Park says he’s confident that the bill for transforming the stadium will not rise any further – but he’s making no guarantees.

Chief executive of the London Legacy Development Corporation David Goldstone said that there was still a year of work to go by contractors Balfour Beatty but it was likely the total £701million bill would stick.

Mostly there was just fitting out work to be completed and not the kind of major engineering challenges that lifted transformation costs to £272million from the original estimate of £154million. The cost included building the largest cantilevered roof in the world.

He was pressed on the bill by members of the London Assembly in light of the rising costs – and the undisclosed “peppercorn” rent to be paid by anchor tenant West Ham.

Chief executive of the London Legacy Development Corporation David Goldstone

Mr Goldstone said: “There still a year’s work to do and I’m not going to give you a guarantee that absolutely nothing would happen that would cost more but I am saying we are confident about the figures we’ve announced.”

Mr Goldstone refused to give details of West Ham’s 99-year lease for reasons of commercial confidentiality and refused to confirm media reports that the rent amounts to just £2.5million a year.

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Assembly member Andrew Boff said: “Don’t you think it’s an enormously good deal for West Ham and not a particularly good deal for us?”

Mr Goldstone responded: “West Ham do have a good deal but I think we have too. Having the stadium at the heart of that park is a really big part of the legacy story. The stadium is absolutely fundamental to all the activity and if it can do that and pay for itself that’s the a good deal for the taxpayer.”