Figure used in bid presentation is revealed for the first time, but Beijing stadium architect predicts price will rise.

The organisers of the London 2012 Olympics have arrived at a budgeted of £275m for the Olympic stadium in east London.

The figure offers an insight into the construction costs of the Olympics, which organisers have not made public. However, reports have suggested that the total construction costs could top £6bn. The government is known to have appointed financial consultant KPMG to keep track of the budget.

Building understands the London bid team used the £275m figure for the stadium in its presentations to the International Olympic Committee in Singapore in July.

Architect J Parrish, a director at design consultant Arup Sport and the man behind the Beijing Olympic stadium designs, has warned that it will be difficult to put a price on the London stadium until a detailed brief has been released and modified by organisers and architects.

The London stadium, widely tipped to be the most problematic to build of the Olympic venues, is likely to have a capacity of about 80,000 seats, reduced to 25,000 after the Games. Parrish said that the costs would not be known until the government made clear the extent to which it was prepared to pay for a stadium with architectural merit or iconic status.

He said: “How do you know what an appropriate cost is? Is it the cost of building a stadium on a temporary basis or is it the cost of the stadium’s iconic Olympic status? The biggest challenge for the design team will be to design for the conversion of the stadium from a first-class venue for the Games to a permanent, breathtaking venue that is financially sustainable in the long term.”

It is understood that architecture practice HOK Sport is working up the design brief with the London Development Agency.

Reports have placed a provisional price tag of £250m on the stadium but Parrish predicts that the costs will increase because of the complex nature of building stadiums.

“The designs for stadiums are hugely sensitive,” he says. “Once on site, changing the designs of, for example, the first row of seats by 100 mm could send costs rising by millions of pounds because changes would need to be made to the viewpoints of all the seats in that section, as well as to the roof and envelope structure.” The roof of the Beijing stadium has just been subject to a late design change to save costs.

Parrish also warned of capacity problems, which he said were often underestimated at Olympic stadium venues. The Beijing stadium, the cost of which has remained secret, was originally designed to hold 100,000 seats but rose to 7000 once media and other facilities were included at a late stage of the design process.