An official appointed by the British Department of Trade and Industry under the Trade Union and Labour Relations (Consolidation) Act 1992, whose main duties concern the supervision of both trades unions and employers' associations, specifically their obligations as bodies corporate to keep accounting records and submit annual returns of audited reports and accounts.
The Certification Officer's most important role is determining whether a trade union or staff association is 'independent' and issuing the appropriate certification as evidence of that 'independence'. But he also has wide ranging powers to investigate the financial affairs of trades unions and to require the production of documents from the union, and is generally responsible for the regulation of trades unions and employers' associations.
Based on information from ACAS at http://www.acas.org.uk/index.html and also http://www.emplaw.co.uk/free/index.htm