The number of staff in the Department's predecessor (Department of Trade and Industry) in 1997 is shown within the Civil Service Statistics 1997 link ‘Civil Service Statistics 1997’ and forms part of the Civil Service statistics archive
http://www.civilservice.gov.uk/about/who/statistics/archived-reports.aspx
The Department for Business, Enterprise and Regulatory Reform (BERR) ceased to exist on 5 June when the Department for Business, Innovation and Skills (BIS) was created from the merger of BERR and the Department of Innovation, Universities and Skills (DIUS).
There are a total of 3,618 staff within BIS as at 30 September.