A spokesperson for the practice denied that this was case, but sources close to the scheme confirmed that there were plans for a tower in Bishopsgate Goods Yard.
News of the proposal is likely to meet a hostile response from heritage groups hoping to stop the Railtrack-owned 4.2 ha site becoming a commercial office area.
Groups such as the Prince's Foundation and English Heritage want to preserve its railway arches and social mix. They fear that this could be lost with too much office development and the construction of the East London Underground Line extension.
This week, the opposing camps were awaiting a government decision on whether to give the site a grade II listing.
The campaign to preserve the area gathered momentum after the Prince of Wales wrote to culture secretary Tessa Jowell recommending that the site be listed.
One campaign source said the Foster plans should be laid out in the open so that the public could be consulted. He said: "If the local community said it wanted a 30-storey tower that only serviced the City then we'd back off, but they aren't going to say that, are they?"
Local businesses are concerned that the redevelopment of the area could involve the demolition of their buildings. Tim Yeo, the shadow culture spokesman, said he had passed on these concerns.
In a further twist, a consortium of local business groups and councils has appointed consultant Arup to draw up an environmental and capacity assessment for the area.
The consortium, which includes the City Fringe Partnership, the Corporation of London, Hackney council and Tower Hamlets council, hopes the assessment will find suitable uses for each part of the site, with a long-term view to create a mixed-use masterplan for the area.
The group is treated with some suspicion by the heritage lobby, largely because of the antagonism between the Corporation of London and EH.