| C. & J. Clark International Ltd | Street |
| Cable & Wireless plc | London |
| Cabot Circus | Bristol |
| Cadbury | Uxbridge |
| CAF (Charities Aid Foundation) | West Malling |
| Cafédirect plc | London |
| Caledonian Brewing Company | Edinburgh |
| Callaway Golf Europe Ltd | Chessington |
| Calypso Soft Drinks Ltd | Wrexham |
| Camelot Group Plc | Watford |
| Camelot Group Plc | Watford |
| Cannon Hygiene Ltd | Morecambe |
| Canoe Association of Northern Ireland | Belfast |
| Canon (UK) Ltd | Reigate |
| Canterbury of New Zealand | Stockport |
| Capespan Ltd | Sheerness |
| Capita Group PLC | London |
| Capital One | Nottingham |
|
Capitalize Ltd | London |
| Carat Sponsorship | London |
| Cardif Pinnacle | Borehamwood |
| Cargill PLC and Banks Cargill Agriculture Ltd | Lincoln |
| Carlsberg UK Ltd | Northampton |
| The Carphone Warehouse PLC | London |
| Castle Cover | Poole |
| Castrol UK Ltd | Swindon |
| Catch Sport | Brentwood |
| Cavendish Hospitality | London |
| CC Group | Reading |
| The Central Council of Physical Recreation (CCPR) | London |
| The Central Council of Physical Recreation (CCPR) | London |
| Centrica plc | Windsor |
| Cereal Partners UK | Welwyn Garden City |
| CEREC (European Committee for Business, Arts & Culture) | 1050 Brussels |
| Challenge Trophies Ltd | Wallington |
| Victor Chandler On Course | London |
| Channel 4 Television | London |
| Channel 4 Television | London |
| Charities Advisory Trust | London |
| Charities Evaluation Services (CES) | London |
| Charities Official Investment Fund (COIF) | London |
| Charities Trust | Liverpool |
| Charity Commission Direct | Liverpool |
| Charity Tax Group | London |
| Chaucer Group | Faversham |
| Cheil Communications Europe Ltd | Chertsey |
| Chelsea and Westminster Health Charity | London |
| Chelsea Building Society | Cheltenham |
| Cheltenham & Gloucester plc | Gloucester |
|
Cheltenham Festivals | Cheltenham |
|
Cheltenham Racecourse | Cheltenham |
| Cheshire Building Society | Macclesfield |
| Chevron Ltd | London |
| Chichester Observer | Chichester |
|
CHILDREN with LEUKAEMIA | London |
| Chiltern Railways Co Ltd | London |
| Chivas Brothers Ltd | London |
| CHR (Conrad Humphreys Racing) | Plymouth |
| Churchill Insurance Company Ltd | Bromley |
| Ciba Specialty Chemicals PLC | Macclesfield |
| Citizen Watch (United Kingdom) Ltd | Wokingham |
| Citroën UK Ltd | Slough |
| Clarion Communications | London |
| Clarion Golf Management & Marketing Ltd | Epsom |
| Classic FM | London |
| The Classic Mineral Water Company | Craigavon |
| Classic Motorcycle Magazine | Horncastle |
| Clay Pigeon Shooting Association (CPSA) | Woking |
| Clerical Medical Investment Group Ltd | Bristol |
| Club Cricket Conference (CCC) | Hampton |
| Clydesdale Bank Plc | Glasgow |
| The Co-operative Bank plc | Manchester |
| Co-operative Group Ltd | Manchester |
| Cobbetts LLP | Birmingham |
| Cobra Beer Ltd | London |
| Coca-Cola Great Britain & Ireland | London |
| Christopher Coley Ltd | Cheltenham |
| Colgate-Palmolive (UK) Ltd | Guildford |
| Collins Stewart Ltd | London |
| Collyer-Bristow Solicitors | London |
| Columbus Direct Travel Insurance | London |
| Commonwealth Games Council for Scotland (CGCS) | Stirling |
| Commonwealth Games Federation | London |
| The Communications Agency Ltd | London |
| Community Development Foundation (CDF) | London |
| Community Links | London |
| Community Self-Build Agency (CSBA) | Sheerness |
| comparethemarket.com | Peterborough |
|
Comperio Research | London |
| Computacenter (UK) Ltd | Hatfield |
| Computeach International Ltd | Dudley |
| Computer Associates PLC | Slough |
| Computer People | London |
| Concept Group Ltd | Livingston |
| Condé Nast Interactive | London |
| The Condé Nast Publications Ltd | London |
| Connexus Group Ltd | London |
| ConocoPhillips | Warwick |
| Consolidated | London |
| Constellation Europe Ltd | Guildford |
| Contemporary Art Society (CAS) | London |
| Continental Sports Ltd | Huddersfield |
| Continental Tyre Group Ltd | West Drayton |
| Cooper Tire & Rubber Company Ltd | Melksham |
| Co-operative Financial Services (CFS) | Manchester |
| Coors Brewers Ltd | Burton-on-Trent |
| Coral Racing Ltd | Barking |
| Corona osp | 15000 Prague 5 |
| The Corporate Responsibility Group | London |
| Costcutter Supermarkets Group | York |
| Cotton Traders Ltd | Altrincham |
| Coty UK Ltd | London |
| Couchman Harrington Associates | London |
| Council for Advancement & Support of Education (CASE Europe) | London |
| The Council for Business & the Arts in Canada | Toronto |
| Countryside Alliance | London |
| Countryside Council for Wales - Cyngor Cefn Gwlad Cymru (CCW) | Bangor |
| Coutts & Co | London |
| Coventry Building Society | Coventry |
| Cowlin Construction Ltd | Bristol |
| Coys | Richmond |
| CPS Fuels Ltd | Norwich |
| Crafts Council | London |
| Credit Suisse Group | Zurich |
| Cricket Scotland | Edinburgh |
| The Croquet Association | Cheltenham |
| Crown Golf | Binfield |
| Crusader Sports | Worcester |
|
Crusaid | London |
| CSV | London |
| CSV Media, London | London |
| Cubeworks | Brighton |
| Cultural Management Unit | Newcastle upon Tyne |
| Cushman & Wakefield | London |
| Cycling Time Trials (CTT) | Leigh |
