| Code Chewing Ltd | Information & communication | 2016 |
| Coega Biomass Processing Limited | Energy | 2020 |
| Coega Hydrogen Limited | Energy | 2020 |
| Coega Solar Park Limited | Energy | 2020 |
| Coffee Nation South Limited | Hospitality | 2025 |
| Coil Maintenance Limited | Manufacturing | 2000 |
| Coleman Roofing & Building Services Limited | Construction | 2019 |
| Colin's Leap Limited | Other services | 2021 |
| Collins Investments Ltd | Real estate | 2023 |
| Coloradical Limited | Professional & scientific | 2023 |
| Colorkote Limited | Construction | 2013 |
| Colour Blaze Limited | Construction | 1999 |
| Comments Disabled Ltd | Education | 2022 |
| Commercial & Domestic Aluminium Ltd | Construction | 2000 |
| Communicate Solutions Limited | Wholesale & retail | 2000 |
| Compass Medical Group Ltd | Wholesale & retail | 2025 |
| Complete Coherence Limited | Professional & scientific | 2004 |
| Complete Pocus Training LLP | | 2024 |
| Complete SKI Limited | Extraterritorial | 2008 |
| Complete Spine Care Limited | Health & social care | 2018 |
| Complete Stair Systems Ltd | Construction | 2005 |
| Complete Window Cleaning Ltd | Administrative & support | 2017 |
| Compute Capital Limited | Financial services | 2025 |
| Connect Construction Services Ltd | Construction | 2005 |
| Constructive Cubism Limited | Health & social care | 2018 |
| CONTESTS4CAUSES Ltd | Information & communication | 2014 |
| Continental Flavors Ltd | Wholesale & retail | 2025 |
| Cool Runners Limited | Manufacturing | 2009 |
| Coolbell Limited | Professional & scientific | 1998 |
| Coopers of Hampshire Limited | Wholesale & retail | 2022 |
| Copia Productions and Communications Limited | Information & communication | 2015 |
| Core Condition Limited | Education | 2009 |
| Core Principle Carpentry Ltd | Construction | 2021 |
| Coritan Ltd | Information & communication | 2026 |
| Cornerstone Cost Consultancy Ltd | Professional & scientific | 2026 |
| Cornlove Limited | Construction | 1974 |
| Cortech Building Services Limited | Construction | 2018 |
| COSEV1 Ltd | Hospitality | 2023 |
| Costec Consultancy Ltd | Professional & scientific | 2021 |
| Cotswold Orthopaedic Group Ltd | Health & social care | 2019 |
| Country Pooch Limited | Other services | 2020 |
| Country Pooch Paddock Hire Limited | Other services | 2026 |
| County Commercial Cars Limited | Wholesale & retail | 1996 |
| County Commercial Engineers Limited | Wholesale & retail | 1996 |
| County Tractor Spares Limited | Administrative & support | 2005 |
| County Tractors Limited | Wholesale & retail | 2010 |
| Covertrade Risk Management Ltd | Financial services | 2022 |
| CP Walking and Home Boarding Limited | Other services | 2024 |
| CP Walking Limited | Other services | 2026 |
| CPG Auto Solutions Ltd | Wholesale & retail | 2022 |
| Crafted Architects Limited | Professional & scientific | 2017 |
| Crafted Buildings Limited | Professional & scientific | 2024 |
| Craftworx Carpentry Ltd | Construction | 2023 |
| Craighill Medical Limited | Health & social care | 2018 |
| Craiglea Limited | Hospitality | 2011 |
| Crampmoor Garage Ltd | Wholesale & retail | 2022 |
| Creative Landscaping Construction Ltd | Administrative & support | 2019 |
| Cremate a Pet South Ltd | Other services | 2026 |
| Crescent Estates (Southampton) Limited | Real estate | 1960 |
| Cribben Southampton Limited | Hospitality | 2018 |
| Cross Oaks Farm Limited | Agriculture & fishing | 2022 |
| Crown Quarters Ltd | Real estate | 2025 |
| Crownstone Capital and Property Ltd | Real estate | 2025 |
| Cryofix Wellness Ltd | Health & social care | 2021 |
| CS7 Networks Limited | Information & communication | 2017 |
| CSI Consulting Limited | Information & communication | 2008 |
| Csrta Limited | Other services | 2025 |
| Cubix Apartments RTM Company Ltd | Households | 2023 |
| Curbridge Motor Company Limited | Wholesale & retail | 1998 |
| Curlews Farm Limited | Real estate | 2007 |
| Curly Marketing Ltd | Professional & scientific | 2017 |
| Cwench Limited | Professional & scientific | 2017 |
| CWS UK Services Ltd | Water & waste | 2021 |
| Cyban Group Ltd | Information & communication | 2021 |
| Cyban Protect Ltd | Information & communication | 2019 |
| Cyban Technologies Ltd | Information & communication | 2021 |
| Cyril's Soap Shed Ltd | Manufacturing | 2019 |
| D & F Building Services Limited | Construction | 2020 |
| D & N White Anaesthesia Limited | Health & social care | 2011 |
| D & R Maintenance Services Ltd | Administrative & support | 2008 |
| D & R Tunney Property Limited | Real estate | 2025 |
| D J Sparkes Limited | Health & social care | 2011 |
| D Neal Limited | Wholesale & retail | 2017 |
| D R Boyce Limited | Wholesale & retail | 2006 |
| D Tunney Limited | Health & social care | 2023 |
| D&T Hampshire Property Services Limited | Administrative & support | 2023 |
| D&T MAN Co Limited | Real estate | 2024 |
| D'Sculpted Ltd | Manufacturing | 2022 |
| D.U.K9. Ltd | Administrative & support | 2022 |
| Daley Hub Limited | Information & communication | 2013 |
| Dalia Ismail Ltd | Real estate | 2019 |
| Dalmeny's Auctioneers Ltd | Administrative & support | 2026 |
| Dancer Consulting Limited | Professional & scientific | 2017 |
| Dandys Ford Farm Ltd | Agriculture & fishing | 2019 |
| Danebury Limited | Professional & scientific | 2016 |
| Danson-Bennett Properties Ltd | Real estate | 2023 |
| Darcy Construction Limited | Construction | 1999 |
| Darcy Homes (South) Ltd | Real estate | 2017 |
| Darksabre Limited | Health & social care | 2023 |
| Dasic Food Hygiene Limited | Manufacturing | 2013 |