The project to organise the London Olympics suffered a setback yesterday when one of its senior figures resigned amid concerns over his health.
Jack Lemley, 71, had served just 11 months of his four-year contract as the chairman of the Olympic Delivery Authority, the body responsible building 2012 venues and infrastructure.
Mr Lemley, from Idaho in the US, was appointed on the strength of his engineering experience, including overseeing the construction of the Channel Tunnel.
A statement from the ODA said he was leaving the £300,000-a-year post because of the increasing workload of his consultancy, Jack Lemley Associates.
Mr Lemley had surgery for arrhythmia, a disorder of the heart's regular beating. He took a month off this May after the operation and returned to work in June.
"I don't know why it took him so long to resign," the London Assembly chairman, Brian Coleman, said. "This is an opportunity to appoint a strong candidate to get the Olympics back on track." Mr Coleman said Mr Lemley's successor should be a Briton.
Mr Lemley said yesterday: "It has been a privilege to chair the ODA for the last year and lead the organisation through its formative stages."