Laing O'Rourke and Sir Robert McAlpine are hoping to reel in a deal to build one of Europe's largest aquariums.
The two firms are expected to find out this month which of them has won the £80 million deal to build Biota!, a 14,500 sq m aquarium designed by Terry Farrell & Partners as part of the Silvertown
Quays development in east London.
The scheme is designed as an underwater equivalent of the Eden Project in Cornwall and will be separated into different habitats representing aquatic ecosystems from around the world.
Developer Silvertown Quays has linked up with Kajima Urban Design and the Zoological Society of London to build the project.
A contractor will be appointed on a two-stage fixed-price design and build deal. The winner will work with the client to develop the project ahead of a start on site in autumn 2008.
One bid source said: "It's a busy market, particularly in the east end of London, given the work that is happening on the Olympics and around the Dome, so the developer might have struggled to get bidders for this, despite its high profile.
"But they seem to have got two of the big boys of the London building market pitching so they must see it as an attractive contract."
The project is the first element of an overall masterplan that will take 15 years to build.
Silvertown Quays is currently putting in place contractors to deliver the infrastructure required to open up the 24 ha site. Plots will then be sold to developers.
The first of these plots includes the Millennium Mills, a former flour mill that will be converted into apartments.
The overall scheme will include 5,000 new homes, 7,600 sq m of offices and 5,570 sq m of restaurants and bars on the site next to London City Airport.