This is the official government reply:
The Government is aware that this is a very sensitive issue and the decision to relocate the allotments was not one that was taken lightly. However, it is necessary for the allotments to be relocated if London is to deliver the Olympic Park for the 2012 Olympic Games and Paralympic Games and the long-term plan for the regeneration of the Lower Lea Valley.
The current site of the Manor Garden allotments is in the heart of the Olympic Park and ground levels at the allotment site will need to change by up to 6 metres. These level changes will form part of the flood risk management of the Lower Lea Valley and create a natural area of reed beds and wildlife habitat. The area the allotments occupy will also be in the middle of what will be a huge construction site for the next few years and it would therefore not be possible for the allotment holders to continue their activities in this environment. It would also not be possible for the allotment holders to have access to the site because it needs to be completely secure.
The space currently occupied by the allotments will form part of a circulation and access area during the 2012 Games. This area is vital for the movement, safety and security of the public during the Games. After the Games it will be one of the key connections in the area, acting as part of the link between the green spaces of the Lea Valley Regional Park, Hackney Marsh and the Olympic Park.
Following the 2012 Games there is a commitment to reinstate at least the same number of allotments within the Legacy Park and all current Manor Garden allotment holders will be offered one of these new allotments. In the meantime the London Development Agency (LDA), which is responsible for assembling the land for the Olympic Park, is working with the allotment holders to try to relocate the Manor Garden society for the period running up to the Games. To achieve this, the LDA has submitted a planning application that, if approved, will allow the creation of new allotments within 1 mile of the existing site.