Sir Robert McAlpine, HBG, Exterior, Laing O'Rourke and Bovis Lend Lease submitted first-stage bids for the scheme, next to Liverpool Street station, to client Prudential on Monday. The five were due to be interviewed for the two-stage, lump-sum deal late this week.
One bidder said the reason the scheme was so sought-after was that speculative office developments had been scarce in recent years.
He said: "Firms are very keen on this one, given the recent market condition." He added that the scheme had given contractors some optimism about the future of the office sector. He said: "It's a sign that the developer market is starting to come back a bit."
Other market sources said this week that other office clients, such as legal firms, would be looking for extra office space in coming months, another indication of a change in the market.
Building reported signs of renewed optimism in the commercial market in London last October, pointing to schemes such as Will Alsop's Palestra building in Southwark, south London, and a Sheppard Robson-designed block in the City as signs of an upturn.
Work is not due to start on the Prudential scheme, designed by architect Hurley Robertson and Associates, until the end of the year.
Two grade II-listed 20th-century buildings at 16-18 Finsbury Circus are to be redeveloped and restored. This will create 26,000 m2 of office space, which will be laid out around a central atrium. The speculative scheme will restore the best features of the early-20th century buildings, including a triple-storey entrance lobby.
The scheme obtained planning permission in 2002, receiving strong support from English Heritage and City Heritage. Other project team members include QS Northcroft, structural engineer Waterman and services engineer Roger Preston & Partners.