This first phase of construction involves reinforcing the ground on which the Stadium will sit by installing up to 4000 concrete columns into the soil. This also forms the permanent foundations for the Stadium's structure.
The event marked the beginning of the big build work across the Olympic Park. Construction will speed up over the next year when works start on the other five main venues: the Aquatics Centre, Velopark, International Broadcast Centre/Main Press Centre and Olympic Village.
Brown said: "The early start to building work on the Olympic Park site is good news, taking us another step closer to 2012 and the regeneration of one of the country's most deprived areas. I have no doubt that the construction of the new permanent venues, infrastructure and transport links, within the largest new urban park to be created in Europe for 150 years, will be a catalyst for lasting social and economic change in east London."
Floor slabs will then be laid for the base of the bowl and the lower-tier structures. Early in 2009, steel structures to support the stadium roof will begin to be installed.
Meanwhile, billions of naturally occurring micro-organisms are helping clean nearly 50,000t of petrol and contaminated soil on the London Olympic Park site so it can be reused to create the urban park.
Bacteria, fungi and other microbes will clean the soil without any waste being taken to landfill as part of the Olympic Delivery Authority's (ODA) green agenda.
The ODA's chief executive David Higgins said: "Cleaning up the Olympic Park is incredibly challenging. We are on track to clean and clear most of the site by Beijing 2008 and meet our sustainability commitments.
"By using the latest technology we are transforming land contaminated by decades of industrial use and neglect into an area fit for world-class sporting venues, a new urban park and the development of new communities."
The micro-organisms in the soil, on the parts of the Olympic Park that has suffered decades of contamination, naturally consume petroleum hydrocarbons such as petrol and diesel.
Warm air, nutrients and water vapour are being pumped through soil in specially constructed bio-remediation beds to massively increase the number of harmless micro-organisms and speed up this natural composting process.
After a few weeks the soil is clean and ready for reuse to create the platform for building venues and parklands for the London 2012 Olympic and Paralympic Games. The bio-remediation work is supporting five soil washing machines that are now cleaning thousands of tonnes of contaminated soil for reuse on site.