| CSH Solution Architecture Ltd | Information & communication | 2018 |
| CSK Assets Ltd | Real estate | 2022 |
| Csrt-Uk Limited | Education | 2024 |
| CSY Construction Limited | Construction | 2014 |
| Cubic Group Ltd | Construction | 2020 |
| Cuddles and Care Day Nursery Ltd | Health & social care | 2024 |
| Cultural Impact Ltd. | Arts & recreation | 2009 |
| Cummins Plumbing & Heating Ltd | Construction | 2012 |
| Cunack Ltd | Extraterritorial | 2024 |
| Cura Recruitment Solutions Ltd | Administrative & support | 2026 |
| Curlew Developments London Ltd | Construction | 2023 |
| Curtis Bros. (Bathrooms) Limited | Construction | 1998 |
| Custom Cabinets Limited | Manufacturing | 2001 |
| Custom Courier Southampton Limited | Transport & logistics | 2017 |
| Custom Interior Wrapping Ltd | Manufacturing | 2025 |
| Customs Clearance Specialists Ltd | Transport & logistics | 2023 |
| Cute Scoops UK Ltd | Wholesale & retail | 2026 |
| Cutover Manager Services Ltd | Information & communication | 2022 |
| Cutting Edge ARB Ltd | Agriculture & fishing | 2001 |
| CW Sports Travel Logistics Ltd | Arts & recreation | 2025 |
| CWM Aggregates Limited | Water & waste | 2017 |
| Cyan Design Limited | Professional & scientific | 1999 |
| Cycle World Wessex Limited | Wholesale & retail | 1991 |
| CYF Ltd | Information & communication | 2020 |
| Cygnet Waste Ltd | Financial services | 2025 |
| Cypress Grove (Chandlers Ford) Residents Limited | Households | 2005 |
| D & K Contracting Services Limited | Construction | 1998 |
| D & Q Southampton Ltd | Real estate | 2021 |
| D Bellard Ltd | Construction | 2021 |
| D C T Solutions Ltd | Financial services | 2025 |
| D J Day Installations Ltd | Construction | 2011 |
| D K & R Properties Limited | Real estate | 2010 |
| D Mooney Fencing Ltd | Administrative & support | 2021 |
| D Rice Installations Limited | Construction | 2016 |
| D S Chase Plumbing & Heating Ltd | Construction | 2023 |
| D&A Tudor Investments Ltd | Real estate | 2022 |
| D&C Goddard Limited | Construction | 2018 |
| D&N Investments Limited | Real estate | 2025 |
| D'Overbroeck's Limited | Education | 1980 |
| D-Mac Consultants Limited | Professional & scientific | 2010 |
| D. Hunt Building Services Ltd | Construction | 2015 |
| D. Jeffery & Co Ltd | Construction | 2006 |
| D. R. Plant Services (Southampton) Limited | Wholesale & retail | 2007 |
| D.A.M. Good Media Limited | Professional & scientific | 2011 |
| D.J. Webb Electrical Services Limited | Construction | 2019 |
| D.J.Harris(Plumbing and Heating)Limited | Construction | 1967 |
| D.M. Woods Limited | Agriculture & fishing | 2015 |
| D.M.C. Autos Ltd | Wholesale & retail | 2024 |
| D.Wolski Limited | Construction | 2019 |
| DA Crowley Ltd | Professional & scientific | 2026 |
| DA Training Services Limited | Education | 2025 |
| Dadu Trans Ltd | Other services | 2019 |
| Dadzie Developments Ltd | Construction | 2021 |
| Daintree Plumbing & Heating Ltd | Construction | 2024 |
| Daisy Nails & Spa Limited | Other services | 2025 |
| Dak'N'Dev Limited | Real estate | 2020 |
| Dala Consulting Group Ltd | Professional & scientific | 2026 |
| Dala Fire & Risk Ltd | Professional & scientific | 2026 |
| Dala Projects Limited | Professional & scientific | 2026 |
| Dala Surveys Ltd | Professional & scientific | 2026 |
| Dale-Sargent Services Ltd | Wholesale & retail | 2025 |
| Dalton’S DEN Limited | Real estate | 2026 |
| DAN Auto Centre Ltd | Wholesale & retail | 2023 |
| DAN Ireson Plumbing & Heating Ltd | Construction | 2019 |
| DAN Mitchell Fitness Limited | Arts & recreation | 2015 |
| DAN the Concrete MAN Limited | Construction | 2021 |
| Dancewise Studios Limited | Arts & recreation | 2012 |
| Dandelion Healthcare Limited | Health & social care | 2021 |
| Danica Payne Business Mentoring Ltd | Administrative & support | 2022 |
| Dante Armaros Tech Ltd | Wholesale & retail | 2020 |
| Darkocean Marine Ltd | Professional & scientific | 2023 |
| Darkside Industry Limited | Manufacturing | 2016 |
| Darren Bundy Limited | Administrative & support | 2015 |
| Darwin Will Co. Limited | Professional & scientific | 1995 |
| Dasic Concrete Cleaning Ltd | Manufacturing | 2015 |
| Dasic Systems Limited | Manufacturing | 2013 |
| Datapro Limited | Administrative & support | 2025 |
| Datasolutionsiq Ltd | Information & communication | 2026 |
| Dave Dodge Photography Ltd | Professional & scientific | 2019 |
| David Bowen Consultancy Ltd | Professional & scientific | 2019 |
| David Coates Limited | Professional & scientific | 2025 |
| David DRY Construction Limited | Construction | 2002 |
| David Stone Properties Ltd | Real estate | 2025 |
| Davies Software Engineering Ltd | Information & communication | 2008 |
| Davis Epos Limited | Information & communication | 2021 |
| Davvat Limited | Professional & scientific | 2017 |
| Dawes Properties Ltd | Real estate | 2001 |
| Dawn Breaking Ltd | Professional & scientific | 2021 |
| Dawn Imaging Ltd | Health & social care | 2021 |
| Day Collier Projects Limited | Construction | 2019 |
| Daybreak Family Group Conferences | Health & social care | 1999 |
| Dazzling Web Planet Limited | Information & communication | 2011 |
| DB Cardiology Limited | Health & social care | 2023 |
| Dbrotas Ltd | Information & communication | 2021 |
| DBT Investments Limited | Financial services | 2022 |
| Dbtr Legal Services Limited | Professional & scientific | 2017 |
| Dbyhundred Ltd | Professional & scientific | 2012 |
| DCN Global Limited | Other services | 2017 |
| DCP Carpentry Limited | Construction | 2018 |
| DE Groot Fresh Produce UK Limited | Administrative & support | 2006 |