The locally based practice saw off bids from HKR and skyscraper supremo Ian Simpson to land the scheme, following a developer-organised design competition (see AJ 03.08.06).
The three practices were approached by property giant Bruntwood to come up with a 4,700m 2building to replace an existing three-storey 1970s block in Fountain Street.
The developer had given the firms just four weeks to come up with a 'cutting-edge design' for the challenging plot.
Speaking before the official announcement which is expected later today, Bruntwood's development director Peter Crowther said: 'We are developing this building as an investment, not to sell. Consequently we [were] looking for long-term flexibility and a design that will look good in 20 years' time.'
He added: 'All three practices used the latitude of the brief to provide very different answers to the questions posed.'
Bizarrely, Stephenson Bell's scheme actually came last in a public poll on north-west-based website www.designfood.co.uk, which asked readers to select their favourite.