| Co-Fire Systems Ltd | Construction | 2022 |
| Coach Chapman Football Development Limited | Education | 2025 |
| Coach Wayland Ltd | Arts & recreation | 2026 |
| Coachhouse Suppliers Limited | Hospitality | 2024 |
| Coaching Hours Ltd | Professional & scientific | 2023 |
| Coachstop Holidays Ltd | Extraterritorial | 2011 |
| Coachstop Ltd | Extraterritorial | 2011 |
| Coal Holdings Corporation Limited | Professional & scientific | 1988 |
| Coast + Capri Ltd | Wholesale & retail | 2020 |
| Coast Facilities Ltd | Other services | 2015 |
| Coastal Fuels Limited | Wholesale & retail | 1988 |
| Coates Construction Essex Ltd | Real estate | 2017 |
| Coattail Publications Ltd | Information & communication | 2021 |
| Coccinelle Limited | Education | 2002 |
| Cochrane & Bines Properties Ltd | Financial services | 2022 |
| Cockle Finance Limited | Financial services | 2018 |
| Coco Lighting Group Limited | Manufacturing | 2019 |
| Coco Nails Essex Ltd | Other services | 2023 |
| Cocoon Creative Limited | Professional & scientific | 2010 |
| Cocoon Digital Studio Ltd | Information & communication | 2018 |
| Cocreate Art Ltd | Arts & recreation | 2018 |
| Cocreate Holdings Limited | Financial services | 2023 |
| Coda Consulting Ltd | Education | 2026 |
| Code Virtue Limited | Information & communication | 2024 |
| CODE.194 Coffee Roasters Ltd | Manufacturing | 2023 |
| Codec Communications Limited | Information & communication | 1997 |
| Codecanvas Studios Limited | Information & communication | 2024 |
| Codementor Network Ltd | Information & communication | 2025 |
| Codepack Solutions Limited | Manufacturing | 1999 |
| Cofan Ltd | Hospitality | 2008 |
| Coffee and Cake at the Close Ltd | Wholesale & retail | 2023 |
| Coffee Carter Limited | Hospitality | 2017 |
| Coffeeroulette Limited | Information & communication | 2021 |
| Cofic Limited | Real estate | 2026 |
| Coga Limited | Administrative & support | 1997 |
| Cogenta Ltd | Financial services | 2018 |
| Colchester Auto Refinishing Supplies Limited | Wholesale & retail | 1991 |
| Colchester City Food Limited | Wholesale & retail | 2026 |
| Colchester GUN Club Ltd | Arts & recreation | 2007 |
| Colchicum Limited | Hospitality | 1998 |
| Cold Chain Solutions Limited | Manufacturing | 2023 |
| Cold Room Network Ltd | Manufacturing | 2025 |
| Cold Start Studios Limited | Professional & scientific | 2025 |
| Coldharbour Contracts Ltd | Other services | 2001 |
| Cole & Co Property Ltd | Construction | 2025 |
| Colecross Limited | Wholesale & retail | 1978 |
| Colipa Ltd | Construction | 2023 |
| COLLABORATION365 Limited | Information & communication | 2018 |
| Collabrii Limited | Professional & scientific | 2022 |
| Collards Upholstery London Limited | Professional & scientific | 2011 |
| Collective Comfort Properties Limited | Real estate | 2025 |
| Collective Markets Ltd | Professional & scientific | 2018 |
| Collective-I Search Ltd | Administrative & support | 2010 |
| Collectors Calibre Limited | Wholesale & retail | 2021 |
| Collier Consultants Limited | Information & communication | 2009 |
| Collins Environmental Ltd | Administrative & support | 2024 |
| Collins UK Estates Ltd | Real estate | 2022 |
| Colman Accountancy Services Ltd | Professional & scientific | 2024 |
| Colne Heritage Assets Limited | Real estate | 2025 |
| Colne Investment Management Ltd | Financial services | 2014 |
| Colne Valley Primary Care Network Limited | Health & social care | 2022 |
| Colne Valley Shipping Limited | Transport & logistics | 2000 |
| Colorlux Ltd | Construction | 2024 |
| Colormagic Ltd | Manufacturing | 2022 |
| Colorminium (London) Ltd | Manufacturing | 2010 |
| Colourfoil Limited | Manufacturing | 1971 |
| Colton & Jones LLP | | 2009 |
| Columb Group Ltd | Financial services | 2023 |
| Columb Limited | Construction | 2016 |
| Columbus Fifty Three Limited | Financial services | 2018 |
| Colwin Group Limited | Construction | 2025 |
| COM Eval Ltd. | Information & communication | 1997 |
| Comanche (UK) Limited | Information & communication | 1999 |
| Combay Limited | Wholesale & retail | 2025 |
| Comberton Flat Management Company Limited | Households | 1983 |
| Comcloud Holdings Ltd | Real estate | 2025 |
| Comcloud IT Services Ltd | Information & communication | 2015 |
| Comicus Ltd | Arts & recreation | 2006 |
| Coming Soon Ltd | Real estate | 2020 |
| Commcise Software Limited | Information & communication | 2015 |
| Commensus Limited | Information & communication | 2008 |
| Commercial Cleaning UK Limited | Administrative & support | 2022 |
| Commercial Evaluations Limited | Information & communication | 2011 |
| Commercial Heating and Plumbing Limited | Construction | 2024 |
| Common Sense Implementations Ltd | Information & communication | 2023 |
| Commonside Properties Limited | Real estate | 2005 |
| Comms Capital Holdings Ltd | Financial services | 2020 |
| Comms Express Limited | Wholesale & retail | 2002 |
| Community Leadership Hub CIC | Education | 2026 |
| Community Tech Hub CIC | Information & communication | 2024 |
| Companies Plus Limited | Professional & scientific | 1998 |
| Company of Proprietors of the Chelmer and Blackwater Navigation Limited | Real estate | 1913 |
| Compare by Review Limited | Information & communication | 2017 |
| Compassion Medical Limited | Wholesale & retail | 2013 |
| Competitive Ship Brokers Limited | Extraterritorial | 2016 |
| Complete Financial Solutions Limited | Financial services | 2004 |
| Complete First AID Ltd | Education | 2026 |
| Complete Heat Ltd | Construction | 2017 |
| Complete PDA Ltd | Administrative & support | 2004 |
| Complete Renewables Ltd | Construction | 2008 |