The largest accountancy firms, both in the UK and globally, are known as the 'Big Four'.
Arthur Anderson had previously been a fifth major firm. Its break-up in 2002, following the collapse of its audit client Enron, saw the 'Big Five' become the 'Big Four'.
Beyond the Big Four, the UK has a substantial number of mid-tier firms and thousands of smaller firms and sole practitioners.
Services provided by the bigger firms include audit, accountancy, tax and legal, corporate finance, business recovery and consultancy. Clients are typically large businesses and government departments. Larger firms have offices throughout the UK and, in some cases, operate globally or belong to international networks.
Smaller firms generally concentrate on one or two service areas, for example accountancy, tax or business advice. They operate in a particular locality or sector. None of the smaller firms offer auditing which is the preserve of the larger firms. Clients include small businesses and the self-employed.
See Accountancy firms and networks for links to more information including surveys, reports and directories.
The history and development of the large firms has been traced by accounting historian Peter Boys. The latest version of his work What's in a name: Firms simplified family trees on the web is published on our web site along with an A-Z index of firms contained in the trees.
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