But details of the project are being kept under wraps because of arguments about funding. Client Railtrack, a subsidiary of national rail company Network Rail, is trying to secure money for the scheme from the Strategic Rail Authority.
A Railtrack spokesperson said: "We have appointed Alsop Architects to do some design work for the station.
"It is looking at redesigning the station and making the concourse bigger. Once we have the design work, we can talk to the Strategic Rail Authority about funding.
"The whole project costs hundreds of millions and we have not got the funding."
New Street is one of the most crowded stations in the country, and an upgrade is seen as vital to Birmingham's regeneration strategy.
The station is surrounded by major redevelopments such as the infamous Bull Ring shopping centre project, but it is badly linked to the rest of the city centre.
A source close to the project said: "The mess around the station is one of the sticking points of the whole regeneration of Birmingham."
Various proposals to improve New Street have been mooted in the past, including a £400m masterplan for the station and its environs abandoned by Railtrack two years ago.