| Clare Bridge Development Limited | Construction | 2023 |
| Clarence Catering Ltd | Hospitality | 2023 |
| Clarion Gate (Chelmsford) Management Company Limited | Households | 2008 |
| Classic Fuel Injection Limited | Wholesale & retail | 2015 |
| Classic Wood Ltd | Construction | 2021 |
| Clay Pigeon Shoot Ltd | Arts & recreation | 2000 |
| Clayworth Imports Limited | Wholesale & retail | 2016 |
| Clean Co (Essex) Limited | Administrative & support | 2017 |
| Cleaning by Tone Ltd | Administrative & support | 2025 |
| Clear Check Testing Limited | Health & social care | 2026 |
| Clear IT Waste Management Ltd | Water & waste | 2026 |
| Clear Port Holdings Limited | Financial services | 2018 |
| Clearway Risk Management Limited | Professional & scientific | 2008 |
| Clearwood Advisory Ltd | Professional & scientific | 2022 |
| Clearwood International Limited | Financial services | 2016 |
| Clemtore Limited | Households | 1982 |
| Click for IT Limited | Administrative & support | 2007 |
| Client Reach AI Ltd | Information & communication | 2025 |
| Clifftown Central Ltd | Hospitality | 2017 |
| Clifftown Investments Limited | Hospitality | 2024 |
| Climatec Group Limited | Financial services | 2024 |
| Clobber Island Ltd | Wholesale & retail | 2025 |
| Cloonmanna Ltd | Agriculture & fishing | 2020 |
| Cloud 9 Business Management Limited | Education | 2011 |
| Cloud Servers UK Ltd | Information & communication | 2025 |
| Clover Environmental Services Limited | Water & waste | 2020 |
| Clover Plant Hire & Sales Ltd. | Administrative & support | 2012 |
| CLW Beauty Limited | Other services | 2012 |
| CM Rapid Testing Solution Ltd | Information & communication | 2014 |
| Cm&P Restaurant Limited | Hospitality | 2024 |
| CMH FAR West Supply Limited | Wholesale & retail | 2024 |
| CMS Communications Ltd | Construction | 2024 |
| CMS Installs Ltd | Administrative & support | 2019 |
| CN Strategies Limited | Extraterritorial | 2003 |
| CNO Systems Limited | Information & communication | 2006 |
| Coast Vending Ltd | Wholesale & retail | 2026 |
| Coastal Cutting Boards Limited | Other services | 2022 |
| Coastal Rest Care Ltd | Health & social care | 2022 |
| Cobham Southend Ltd | Real estate | 2020 |
| Coco Bronze Beauty House Limited | Other services | 2025 |
| Coconuts Hair Studio Ltd | Other services | 2003 |
| CODE2COACHING Ltd | Arts & recreation | 2025 |
| Coffee Industries Ltd | Hospitality | 2021 |
| Coffee Mama Ltd | Manufacturing | 2024 |
| Coininn Games Limited | Arts & recreation | 2004 |
| Colchester Property Ltd | Real estate | 2015 |
| Colectivo Futuro Ltd | Arts & recreation | 2012 |
| Coleman Land Management Company Limited | Households | 2013 |
| Coles Education Solutions Limited | Professional & scientific | 2015 |
| Collabot Legal Limited | Professional & scientific | 2026 |
| Collapse Breeze Air Ltd | Energy | 2025 |
| Collective Inspirations Limited | Wholesale & retail | 2017 |
| Colley Property Ltd | Real estate | 2023 |
| Collins Consultancy Ltd | Professional & scientific | 2024 |
| Colourpassion Ltd | Manufacturing | 2020 |
| Colt Marketing Ltd | Professional & scientific | 2026 |
| Come to Good Properties Ltd | Real estate | 2025 |
| Comedy in the Clubhouse Ltd | Arts & recreation | 2025 |
| Comfit Global Ltd | Wholesale & retail | 2025 |
| Comfortable Heating Ltd | Professional & scientific | 2025 |
| Commercial Services Limited | Manufacturing | 2003 |
| Commisceo Health & Wellness Services Limited | Health & social care | 2025 |
| Commisceo Primary Care Solutions Limited | Administrative & support | 2014 |
| Commissioning Access Limited | Construction | 2021 |
| Company HQ Barbering Academy Limited | Education | 2024 |
| Company HQ Limited | Other services | 2016 |
| Compass House of Refuge Ltd | Education | 2019 |
| Complete 24 Ltd | Other services | 2011 |
| Complete Trading Ltd | Wholesale & retail | 2025 |
| Compliance First Solutions Limited | Construction | 2024 |
| Comptons Cars and Commercials Ltd | Administrative & support | 2009 |
| Computer Network Specialists Limited | Information & communication | 2007 |
| Computers-On-Sea Limited | Information & communication | 2003 |
| Concept - UK Enterprise Limited | Real estate | 2018 |
| Concept Motors Limited | Wholesale & retail | 2013 |
| Concise Residential Management Ltd | Real estate | 2018 |
| Coniston West Park Management Company Limited | Households | 1983 |
| Conkenz Introductions Ltd | Wholesale & retail | 2023 |
| Connectncollect Ltd | Wholesale & retail | 2026 |
| Connor Maggie Properties Ltd | Real estate | 2021 |
| Conpless Marine Limited | Wholesale & retail | 2026 |
| Conquest Electrical Installation Services Ltd | Construction | 2011 |
| Conquest Property Development Ltd | Construction | 2025 |
| Conservas Bates Ltd | Professional & scientific | 2016 |
| Consociato Limited | Real estate | 2001 |
| Construction Buying Services Limited | Professional & scientific | 2015 |
| Construction Risk Management Solutions Limited | Professional & scientific | 2026 |
| Consult US 365 Ltd | Professional & scientific | 2024 |
| Consultancy and Training Solutions Limited | Education | 2004 |
| Continental Express Limited | Transport & logistics | 1933 |
| Contractor Consultancy Services Limited | Professional & scientific | 2011 |
| Contrast Limited | Construction | 2001 |
| Cool Mechanical Services Limited | Construction | 2021 |
| Cool Wash Ltd | Wholesale & retail | 2022 |
| Cooper Accountancy Limited | Professional & scientific | 2024 |
| Cooperman Limited | Financial services | 2017 |
| Coopers Edge (NO 2) Management Company Limited | Households | 2007 |
| Coordinates Label Ltd | Wholesale & retail | 2020 |
| Copacabana Leisure Limited | Hospitality | 2012 |
| Copper Hills Management Company Limited | Households | 2021 |