| Christmas Time Gift Shop Limited | Wholesale & retail | 2023 |
| Christy Floodlighting Limited | Manufacturing | 1985 |
| Christy Lighting Masts Limited | Manufacturing | 1997 |
| Church Lane Apartments Limited | Real estate | 2014 |
| CIM Global Ltd | Information & communication | 2023 |
| Cinema Lightboxes Ltd | Wholesale & retail | 2022 |
| Citizens Advice Essex Limited | Information & communication | 2007 |
| Citrus Events Ltd | Information & communication | 2021 |
| City (R & D) Limited | Extraterritorial | 2001 |
| City Psychologists Limited | Extraterritorial | 2021 |
| City Special Metals Ltd | Manufacturing | 2001 |
| Citytown Group Limited | Extraterritorial | 2001 |
| CJP Sweeney Limited | Financial services | 2024 |
| CJT Pubs Ltd | Hospitality | 2018 |
| Clarity Network Group Ltd | Information & communication | 2018 |
| Claroud Co., Ltd. | Administrative & support | 2024 |
| Classic Bloodstock & Equine Ltd | Financial services | 2025 |
| Clatworth Ltd | Professional & scientific | 2024 |
| Clay Interactive Limited | Professional & scientific | 2007 |
| Claydon Commercial Limited | Real estate | 2007 |
| Claydon Land Development Ltd | Construction | 2007 |
| Clean for Ease Limited | Administrative & support | 2021 |
| Clearvu Windows Ltd | Administrative & support | 2020 |
| Click Accountants Ltd | Professional & scientific | 2018 |
| Climate Consultancy Ltd | Professional & scientific | 2015 |
| Clipheart Ltd | Professional & scientific | 2020 |
| Clockwork Penguin Ltd | Education | 2026 |
| Cloud 10 Flotation & Spa Limited | Information & communication | 2019 |
| Cloughton Court Management Company Ltd | Real estate | 2023 |
| Club-Subs Network Limited | Information & communication | 2018 |
| Clumsies Limited | Hospitality | 2026 |
| CNB Entertainment Ltd | Administrative & support | 2020 |
| CNB Property Solutions Limited | Financial services | 2021 |
| Coalesce Digital Ltd | Professional & scientific | 2025 |
| Cobrasand Ltd | Professional & scientific | 2001 |
| Cockfield Investments Ltd | Real estate | 2025 |
| Coco's Childminding and Daycare Limited | Health & social care | 2024 |
| Coco's Childminding Limited | Health & social care | 2018 |
| Cofris Limited | Professional & scientific | 2009 |
| Cohen & Wilks Limited | Wholesale & retail | 1974 |
| Coherent Leadership Ltd | Professional & scientific | 2026 |
| Colchester Bar and Lounge Ltd | Hospitality | 2026 |
| Colchester Car Hub Ltd | Wholesale & retail | 2024 |
| Colchester Development Limited | Construction | 2019 |
| Colchester Glass Ltd | Extraterritorial | 2025 |
| Colchester Tractors Investments Limited | Real estate | 2016 |
| Cold Norton Community Land Limited | Real estate | 2011 |
| Coleman & Clarke Limited | Professional & scientific | 2005 |
| College Place Limited | Construction | 2014 |
| Collins Education Ltd | Financial services | 2025 |
| Colosseum Bristol Limited | Hospitality | 2023 |
| Coltech Environmental Ltd | Professional & scientific | 2021 |
| Commodity Processing Systems Limited | Wholesale & retail | 2001 |
| Common Cause Communications Ltd | Professional & scientific | 2025 |
| Community Care Partners UK Ltd | Administrative & support | 2026 |
| Compactfield Limited | Real estate | 1983 |
| Comtalk (Leasing) Limited | Administrative & support | 1967 |
| Concepts in Metal Limited | Manufacturing | 2011 |
| Concrete Decarbonisation Network (CDN) LLP | | 2025 |
| Conduit Financial Planners Limited | Professional & scientific | 2025 |
| Conduit IT Services Limited | Information & communication | 2008 |
| Confidence in Clinic Ltd | Education | 2025 |
| Confreight (UK) Limited | Extraterritorial | 2001 |
| Congreve Financial Consultants Limited | Professional & scientific | 2020 |
| Congreve Lims Services Ltd | Professional & scientific | 2022 |
| Congreve Property Developments Limited | Extraterritorial | 2017 |
| Congreve Property Holdings Limited | Real estate | 2017 |
| Connaught Interior Design Limited | Financial services | 2021 |
| Connect 2U Recruitment Ltd | Professional & scientific | 2021 |
| Connexushub Ltd | Information & communication | 2025 |
| Constable PUB Company Limited | Hospitality | 2010 |
| Construction and Roadways Limited | Wholesale & retail | 2025 |
| Construction BID Limited | Professional & scientific | 2023 |
| Cool Down Solutions Limited | Energy | 2011 |
| Coolheat Services Ltd | Energy | 2001 |
| Coollava Limited | Manufacturing | 2010 |
| Cooney Group Ltd | Administrative & support | 2015 |
| Cooney Insulations Limited | Administrative & support | 2009 |
| Cooney Leisure Ltd | Hospitality | 2025 |
| Core Lift Service Ltd | Construction | 2018 |
| Corporate Management Resources Ltd | Professional & scientific | 2002 |
| Corventive Limited | Administrative & support | 2018 |
| Cosgrove Builders & Developers Ltd | Construction | 2019 |
| Cosgrove Land Management Ltd | Financial services | 2025 |
| Cosgrove Property Developments Ltd | Construction | 2022 |
| Cosy Developments Group Limited | Construction | 2024 |
| Cottrell Brickwork.Ceramics Limited | Construction | 2000 |
| Countess Seeds Limited | Wholesale & retail | 1995 |
| Courier Elite Limited | Transport & logistics | 2001 |
| Court House Developments Limited | Construction | 2022 |
| Courtsports Surfaces Limited | Construction | 2023 |
| Cousins Material House Limited | Wholesale & retail | 2003 |
| Cousins Trading Group Limited | Financial services | 2019 |
| Covered Storage Limited | Transport & logistics | 2017 |
| Cozy Escapes Ltd | Real estate | 2025 |
| CPW Property Ltd | Real estate | 2021 |
| CR3 Logistics Limited | Transport & logistics | 2025 |
| CR3 Recruitment Limited | Administrative & support | 2022 |
| Craft Beer Maldon Ltd | Hospitality | 2024 |
| Craig & Paul Holdings Limited | Real estate | 2020 |