The plans by architects Austin-Smith:Lord include restoring the Grade II-listed parts of the building which date back to 1850 and installing IT equipment and an archive.

Other features of the scheme include a rooftop terrace, a conservation studio for repairing historic books and five new floors with meeting rooms and a cafe.

Construction firm Shepherd is the lead contractor in the Inspire Partnership consortium appointed on the work. Asset managers Amber Infrastructure, architects Austin-Smith:Lord, Buro Happold, building services engineers and Cofely on facilities management, make up the rest of the construction and design team.

Work is expected to start on site in June 2010.