An agreement has been signed between the DTI and the Wellcome Trust to push ahead with the high-tech, doughnut-shaped building.
The laboratory is designed by consultant Jacobs Gibb, which won an architectural competition for the scheme last year. The facility is due to be completed by 2006.
It will house a synchrotron machine, which emits ultraviolet and X-ray light beams of exceptional brightness, to study the structure of matter and material in medical research and other fields.
A source close to the scheme said a joint venture firm set up by the Wellcome Trust and the DTI aimed to appoint a contractor in the summer. The joint venture firm will be called Diamond Light Source. The project team already includes project manager Symonds.
The source said: "We are looking to gain Treasury approval for the project in the next few months, then we can start looking for contractors."
The DTI intends to retain strict control over the scheme to avoid a repeat of the problems at the National Physical Laboratory in Teddington, south-west London. Specification problems at the NPL led to £75m losses for contractor Laing last year.
"We are making a big effort to avoid the standard pitfalls of government projects," the source added. "We are implementing an electronic financial system to put firm management tracking into place."
The source said the laboratory would have to be carefully designed to avoid any vibration, which would deflect the laser beams: "We will be working with laser beams that are the thickness of hair strands. The floor will have to be incredibly stable."
The building will form part of the Rutherford Appleton Laboratory, owned by the Council for the Central Laboratory of the Research Councils. The council is an independent public body of the DTI's Office of Science and Technology.
The agreement for the scheme was signed by the Wellcome Trust and the DTI at the end of last month. The DTI was advised by lawyer Nicholson Graham & Jones.