Argent is understood to be inviting tenders for 1m sq ft of office buildings, which will range in height from seven to 11 storeys, with the aim of starting on the project this year.

It will be one of the biggest office jobs to break ground in London in 2013 and has sparked interest among the capital’s major office builders including Mace, Laing O’Rourke and Sir Robert McAlpine.

Bam, Carillion and Kier are Argent’s trio of preferred contractors for jobs on the King’s Cross Goods yard site and they are also tracking the project which has been cloaked in secrecy.

The £700m property deal unveiled yesterday ends months of negotiation between Argent and Google. It means that 4.5m sq ft of the total 8m sq ft and over 50% of the commercial space at King’s Cross is now completed or committed.

David Partridge, director at Argent (King’s Cross), said today: “It is a great privilege to take forward what we believe is London’s largest office requirement in recent years.

“The team led by Nick Searl have done a brilliant job to get this over the line and are very excited by the opportunity to design and build a world class, sustainable HQ for one of the world’s leading companies.

“This is clearly a major step in delivering our vision for King’s Cross and will provide a catalyst for developing the next phase of this unique 67 acre central London location, which will create around 35,000 jobs and deliver over 1,900 new homes.”

Davis Langdon is acting as cost consultants on the project.

Architects Allford Hall Monaghan Morris  has developed sustainable design concepts for the new Google headquarters.

The building will sit above retail space providing a diverse range of shops, cafes and restaurants.

HQ will be located in five buildings tucked in just to the north of the Western Concourse at King’s Cross. The massings shown are only illustrative.