| Bwellhealth Ltd | Health & social care | 2025 |
| BWL Management Limited | Information & communication | 2016 |
| Bwlch Mawr Limited | Information & communication | 2024 |
| BWR Recruitment Limited | Administrative & support | 2016 |
| Bwtuc (Trading) Limited | Hospitality | 1985 |
| BY HIS Grace Sisterhood CIC | Other services | 2025 |
| BY TOR Consulting Ltd | Financial services | 2020 |
| By-Air Conditioning Limited | Construction | 2003 |
| BYA Properties Ltd | Real estate | 2026 |
| Byers Cabling Solutions Ltd | Construction | 2025 |
| Byfield Electrical Services Ltd | Construction | 2024 |
| BYM Infinity Limited | Information & communication | 2026 |
| Byrhtnoth Defence Limited | Public administration | 2025 |
| Byron View Management Company Limited | Real estate | 2017 |
| Byte Labs Ltd | Information & communication | 2023 |
| Bywater Barn Properties Holdings Limited | Real estate | 2021 |
| Bywater Barn Properties Limited | Real estate | 2021 |
| BZM Engineering Limited | Construction | 2024 |
| C & B (Eastern) Limited | Administrative & support | 2009 |
| C & B Frames Ltd | Construction | 2018 |
| C & B Property Services Limited | Real estate | 2020 |
| C & C Metalworks Ltd | Construction | 2019 |
| C & D Dennis Limited | Manufacturing | 2022 |
| C & D Slade Properties Ltd | Real estate | 2025 |
| C & J Tours Limited | Transport & logistics | 2003 |
| C & K Developments Limited | Construction | 2002 |
| C & R Plumbing and Heating Contractors Limited | Construction | 2007 |
| C & S Construction (Colchester) Limited | Construction | 2005 |
| C & S Mathews Ltd. | Wholesale & retail | 2004 |
| C and P Constantine Ltd | Information & communication | 2021 |
| C Bragg & Co. Limited | Professional & scientific | 2009 |
| C Brooks Limited | Health & social care | 2003 |
| C C Consulting (UK)) Ltd | Professional & scientific | 2010 |
| C C Hire Limited | Administrative & support | 2003 |
| C Checklist Limited | Professional & scientific | 2024 |
| C Day & SON (West Mersea) Ltd | Construction | 2002 |
| C E Beauty Ltd | Other services | 2017 |
| C E Mark Consultancy Limited | Extraterritorial | 2002 |
| C G EYE Limited | Professional & scientific | 2004 |
| C Harrison Management Ltd | Construction | 2019 |
| C J Appliances Ltd | Manufacturing | 2015 |
| C J Brooks the Jewellery Workshop Limited | Manufacturing | 2003 |
| C J Cairns Associates Ltd | Professional & scientific | 2019 |
| C J Conway Building and Property Services Ltd | Construction | 2019 |
| C J Drainage Clearance Limited | Water & waste | 2024 |
| C K Jewellers Ltd | Other services | 2018 |
| C M Business Solutions Ltd | Financial services | 2024 |
| C M Chiropractic Ltd | Health & social care | 2012 |
| C Murphy Construction Ltd | Construction | 2025 |
| C Sparling Therapy Ltd. | Professional & scientific | 2015 |
| C V Alozie Limited | Information & communication | 2025 |
| C W Commerce Limited | Wholesale & retail | 2013 |
| C&J Highwoods Homes Limited | Real estate | 2017 |
| C&J Highwoods IT Services Ltd | Information & communication | 2015 |
| C&K (Contracts) Limited | Construction | 2015 |
| C&P Construct Ltd | Construction | 2018 |
| C. and C. Law Limited | Extraterritorial | 1991 |
| C. S. Mason Contracts Limited | Construction | 2001 |
| C. Shield Limited | Other services | 2011 |
| C. Wood Business Services Ltd | Health & social care | 2024 |
| C.C. Discount Heating Limited | Wholesale & retail | 1977 |
| C.Coco Ltd | Health & social care | 2022 |
| C.D.D. (Project Management) Limited | Extraterritorial | 1985 |
| C.J. FOX Building Limited | Other services | 2006 |
| C.J.B Electrical Systems Ltd | Construction | 2014 |
| C.M. Cadman Group Limited (the) | Construction | 1975 |
| C.R Social Care Limited | Hospitality | 2013 |
| Ca&A Limited | Other services | 2026 |
| CAB2GO -Colchester Limited | Transport & logistics | 2024 |
| Caba Accountancy & Taxation Services Limited | Professional & scientific | 2023 |
| Cablers Group Ltd | Financial services | 2022 |
| Cablestore Limited | Extraterritorial | 2022 |
| Cableteq Ltd | Construction | 2020 |
| Cacao Artisans (UK) Ltd | Wholesale & retail | 2015 |
| Cactus Fire & Safety Ltd | Professional & scientific | 2021 |
| Cactus Production Events Ltd | Manufacturing | 2024 |
| CAD Bureau Southern Limited | Information & communication | 2002 |
| CAD Tech Van Systems Limited | Professional & scientific | 2023 |
| Cadence Group Limited | Financial services | 2025 |
| Cadenza United Kingdom Limited | Information & communication | 2000 |
| Cadju Limited | Information & communication | 2015 |
| Cadman 2018 Ltd | Financial services | 2018 |
| Cadman and SON LLP | | 2006 |
| Cadman Construction Limited | Construction | 1975 |
| Cadman Cranes Limited | Construction | 2004 |
| Caesar Court (Colchester) RTM Company Limited | Households | 2015 |
| Cafe Asia Limited | Construction | 2021 |
| Cafe Flavour Limited | Hospitality | 2025 |
| Cafe G Limited | Hospitality | 2003 |
| Cafe Malabar Ltd | Hospitality | 2023 |
| Cafe Plus@Middleborough Ltd | Hospitality | 2024 |
| CAFE21 TG Ltd | Hospitality | 2024 |
| Cafelato Ltd | Hospitality | 2023 |
| Caffe Sala Ltd | Wholesale & retail | 2025 |
| Cahill Company Limited | Real estate | 2020 |
| Cahill Corporation Limited | Construction | 2013 |
| Cahill Holdings Limited | Financial services | 2003 |
| Cakkei International Management Consultancy Limited | Professional & scientific | 2015 |
| CAL Smith Conservation Framing Ltd | Manufacturing | 2020 |
| Calda Systems Ltd | Wholesale & retail | 2022 |