The developer is due to agree a fixed price with contractor Sir Robert McAlpine for the Esso Glen project this week.
The EPR-designed office block is the largest speculative office development to be launched in London in recent months.
McAlpine is due to start on site on 20 January. The contractor beat off Australian rival Multiplex earlier this year to win the first-stage tender for the scheme, which includes 53,000 m2 of offices and 4600 m2 of retail space.
The developer said it was hoping that completion of the scheme, in early 2005, would coincide with an upturn in the office market. Developers are expecting demand for office space to rebound in 2004.
Land Securities project director Derek Baillie said: "We are keeping our fingers crossed that the market will see the other side by then – but who's to say?"
Baillie added that the scheme, originally unveiled in 2000, had taken time to get off the ground because of the complexities of the site, which sits above a tunnel for the District and Circle underground lines.
The developer reached agreement with London Underground this week to build above the tunnel, which was dug in the 1870s. Baillie said: "The risk is huge in terms of potential disruption on that." He added that Land Securities had a project insurance policy to cover such risks.
The team working on the project includes structural engineer Arup, M&E engineer FaberMaunsell, acoustic consultant Hann Tucker, QS Gardiner & Theobald and planning supervisor PCM. Demolition contractor Brown and Mason has started to remove three buildings on the site – Elliott House, Esso House and Glen House – to make way for the development.
The office will be built using the prefabrication techniques used on Laing O'Rourke's headquarters, which is next door.