The decision almost certainly kills off Studio E Architects' ambitious proposals to transform the derelict block behind County Hall into a new 'green island'.
On Tuesday, Lambeth council's planning committee approved this 15-storey development on the roundabout in Westminster Bridge Road.
BUJ now awaits the final thumbs-up from the Greater London Authority for the scheme - which will include conference facilities, a gym, shops, a restaurant and a café.
Originally occupied by the old Greater London Council, the concrete office building has stood empty for years and speculation has been rife about the future of the site. Lambeth had already granted permission for another 13-storey scheme hotel on the site.
Following the decision, work will begin to divert services from under the new building to allow the development to start on site within 15 months.
It is hoped the scheme, which is backed by developer Marlbray, will be completed by January 2010.