| Cleaner Industries Limited | Wholesale & retail | 1985 |
| Cleaning Time Limited | Administrative & support | 2015 |
| Clearaway Clearances Limited | Transport & logistics | 2026 |
| Clearaway Essex Ltd | Water & waste | 2023 |
| Clearer Audio Ltd | Manufacturing | 2004 |
| Clearview Endoscopy Limited | Manufacturing | 2014 |
| Clearview Medtech Limited | Financial services | 2023 |
| Clearview Ultrasound Service Limited | Manufacturing | 2024 |
| Cliff House (Westcliff on Sea) Management Limited | Households | 2005 |
| Clipper & GUY Ltd | Other services | 2024 |
| Cliq Limited | Manufacturing | 2003 |
| Cloc Book Print Limited | Manufacturing | 2021 |
| Cloud Support Limited | Information & communication | 2011 |
| CLW Event Design Limited | Other services | 2020 |
| CMG Roofing Limited | Construction | 2018 |
| CMR Controls Limited | Manufacturing | 1978 |
| CMR Europe Limited | Professional & scientific | 1993 |
| CMR International Limited | Professional & scientific | 1996 |
| CMR Manufacturing Limited | Professional & scientific | 1996 |
| CMR UK Limited | Professional & scientific | 1996 |
| Coastal Camping UK Ltd | Hospitality | 2022 |
| Cobra International Trading Limited | Professional & scientific | 2010 |
| Coco Ramsden Properties Limited | Households | 2025 |
| Cogs Brand Co Ltd | Administrative & support | 2024 |
| Cogs+ Limited | Administrative & support | 2017 |
| Coil (Pro) Solutions Limited | Administrative & support | 2019 |
| Collections Collective Limited | Other services | 2026 |
| Collingwood Consultancy Limited | Information & communication | 2007 |
| Command D Limited | Professional & scientific | 1994 |
| Command P Limited | Hospitality | 2021 |
| Commercial PSV Limited | Manufacturing | 2003 |
| Compass Project Management Ltd | Professional & scientific | 1998 |
| Complete Office Solutions Ltd | Professional & scientific | 2023 |
| Compliance Hydraulics & Safety Limited | Professional & scientific | 2024 |
| Complimentary Sports Calendars Ltd | Professional & scientific | 2024 |
| Compound Creative Arts Ltd | Arts & recreation | 2018 |
| Conceptual Living Consultancy Limited | Construction | 2016 |
| Connah Goldsworthy (Hadleigh) Ltd | Professional & scientific | 2003 |
| Connect Aerials Limited | Other services | 2010 |
| Constructedconcepts Ltd | Real estate | 2025 |
| Consultitech Limited | Other services | 2014 |
| COR Haulage Ltd | Transport & logistics | 2024 |
| Corderoy Advisory Limited | Information & communication | 2025 |
| Corien Bidelta Consulting Limited | Real estate | 2017 |
| Cornerhouse Property Management Limited | Real estate | 2020 |
| Corporate Cameo Limited | Professional & scientific | 2017 |
| Corr Industrial Flooring Ltd | Construction | 2026 |
| Cosmo Industries UK Ltd | Professional & scientific | 2008 |
| Cottis House Limited | Real estate | 1973 |
| County Hydraulics and Radiators Ltd | Manufacturing | 2025 |
| Covert Tech Limited | Wholesale & retail | 2017 |
| Cozydoze Ltd | Wholesale & retail | 2019 |
| CPL Maps & Media Ltd | Information & communication | 2021 |
| Craig Hewitson Limited | Professional & scientific | 2008 |
| Craven Foods (UK) Limited | Hospitality | 2025 |
| Crayford Automobiles Ltd | Manufacturing | 2022 |
| Crazy Castles Essex Ltd | Administrative & support | 2025 |
| Created Especially for YOU Limited | Wholesale & retail | 2020 |
| Crest Coaches Limited | Transport & logistics | 2005 |
| CRG Retail Ltd | Wholesale & retail | 2024 |
| Cripps Brothers Limited | Real estate | 2019 |
| Croftlive Ltd | Hospitality | 1999 |
| Cronos Internet Ltd | Information & communication | 2012 |
| Crouch Shipping Agency Limited | Transport & logistics | 1999 |
| Crown Kitchens & Interiors Limited | Manufacturing | 2018 |
| Crowstone Road Management Co. Ltd. | Households | 1990 |
| Cryptobee Limited | Information & communication | 2024 |
| CS Commercial Flooring Ltd | Construction | 2025 |
| CSL Yard Ltd | Real estate | 2025 |
| CT Coaching Limited | Administrative & support | 2016 |
| CTH Consultancy Ltd | Professional & scientific | 2023 |
| Cultural Engine (UK) Limited | Professional & scientific | 2014 |
| Curate Prosperity Ltd | Financial services | 2024 |
| Curr Property Management Limited | Other services | 2006 |
| Currency Farm Limited | Financial services | 2018 |
| Curry Cafe 2026 Limited | Hospitality | 2024 |
| Curtis Electrical Contracting Services Ltd | Construction | 2024 |
| Custom Air Conditioning Limited | Construction | 2022 |
| Cybersecskills Ltd | Information & communication | 2026 |
| Cynq AI Ltd | Information & communication | 2025 |
| Cystall Clear Cleaning Limited | Administrative & support | 2025 |
| D & C Nails Ltd | Other services | 2025 |
| D & D Property Consultancy Services Ltd | Professional & scientific | 2024 |
| D & D Protection Engineering Ltd | Information & communication | 2012 |
| D Dewis Plumbing & Heating Ltd | Construction | 2016 |
| D F Electrical Essex Ltd | Construction | 2022 |
| D J F Electrical Contracting Services Limited | Construction | 2011 |
| D&C Ferns Property Ltd | Real estate | 2023 |
| D&F Utilities Ltd | Construction | 2023 |
| D&H Drinks Wholesale Ltd | Wholesale & retail | 2023 |
| D.I. Styles Ltd | Financial services | 2003 |
| D.O.R.C. Limited | Manufacturing | 2011 |
| Dagistan Electrical Ltd | Professional & scientific | 2021 |
| Dalton Window Cleaning Ltd | Administrative & support | 2018 |
| DAN Kitchener Art Ltd | Arts & recreation | 2024 |
| Daniel Gibbard Architectural Design Ltd | Professional & scientific | 2015 |
| Daniel James Flooring Limited | Wholesale & retail | 2012 |
| DAR Pharma Limited | Wholesale & retail | 2014 |
| Dave’S Plumbing & Heating Ltd | Construction | 2026 |
| Davison Group Developments Limited | Real estate | 2025 |