| Circuit Group Limited | Financial services | 2007 |
| Circuit Supply Limited | Wholesale & retail | 1999 |
| Circular Computing Limited | Extraterritorial | 2019 |
| Cirrom Ltd | Information & communication | 2021 |
| CIS Solved Limited | Wholesale & retail | 2026 |
| Citea Outlets Ltd | Wholesale & retail | 2022 |
| Citi Consultancy Ltd. | Real estate | 2014 |
| Citi Partners Consultants LLP | | 2013 |
| Citizens Advice Hampshire | Other services | 2007 |
| Citizens Advice Solent East | Professional & scientific | 1994 |
| Citrus UK Holdings Limited | Administrative & support | 2024 |
| City & County Securities Limited | Administrative & support | 1996 |
| City Accountant Portsmouth Limited | Professional & scientific | 2014 |
| City Arts Portsmouth Community Interest Company | Health & social care | 2023 |
| City Damp Solutions Ltd | Construction | 2017 |
| City Exhaust and Tyres Ltd | Wholesale & retail | 2002 |
| City Group Accountant Limited | Professional & scientific | 2025 |
| City Heat Portsmouth Ltd | Other services | 2017 |
| City of Portsmouth College Enterprises Ltd | Extraterritorial | 1995 |
| City Properties and Management Limited | Real estate | 2018 |
| City Room 4 Rent Limited | Real estate | 2020 |
| City Umbrella Co Ltd | Professional & scientific | 2017 |
| Cityev Ltd. | Manufacturing | 2011 |
| Citymain Administrators Limited | Financial services | 2000 |
| Citymain Limited | Wholesale & retail | 2009 |
| Ciurkot Limited | Construction | 2025 |
| CJ Estates Ltd | Real estate | 2015 |
| Cjdb Electrical Services Ltd | Construction | 2017 |
| CJH & Sons Roofing Ltd | Construction | 2025 |
| CJM SKI and Wake Limited | Arts & recreation | 2014 |
| CJN Recycling Limited | Administrative & support | 2023 |
| CJP Electrical Contractors Ltd | Construction | 2018 |
| CJS Construction Services Ltd | Construction | 2023 |
| CJS Environmental Limited | Water & waste | 2006 |
| CJS Holdings Limited | Professional & scientific | 2002 |
| CJS Portsmouth Limited | Wholesale & retail | 2002 |
| CK Ventures Limited | Administrative & support | 2010 |
| CKO Limited | Professional & scientific | 2018 |
| Cladded Industrial Buildings Limited | Construction | 2024 |
| Cladding Services Southern Ltd | Construction | 2024 |
| Cladiatorz Limited | Construction | 2022 |
| Cladify Services Ltd | Construction | 2026 |
| Claims Recruitment Services Limited | Administrative & support | 2013 |
| Claire Mace Nutrition Ltd | Administrative & support | 2023 |
| Claire's Floristry Limited | Wholesale & retail | 2018 |
| Clameg Design and Build Ltd | Construction | 2010 |
| Clameg Projects Ltd | Construction | 2026 |
| Clapback Ltd | Wholesale & retail | 2023 |
| Clare Terrace Investment Company Limited | Real estate | 1960 |
| Claremont Lodge (Southsea) Limited | Households | 2016 |
| Clarence Management Ltd | Real estate | 2021 |
| Clarence Road Gosport Limited | Real estate | 2024 |
| Clares Business Solutions Limited | Professional & scientific | 2007 |
| Clares Office Supplies Limited | Wholesale & retail | 1972 |
| Clarity Health Apex Ltd | Health & social care | 2026 |
| Clarity Mortgage Services Limited | Financial services | 2018 |
| Clarity North Ltd | Wholesale & retail | 2017 |
| Clarity Vision (Group) Limited | Administrative & support | 1997 |
| Clarius Trust Ltd | Information & communication | 2025 |
| Clarke Quantity Surveyors Ltd | Professional & scientific | 2023 |
| Classic Carpets (Portsmouth) Limited | Wholesale & retail | 2001 |
| Classic Restoration and Services Limited | Wholesale & retail | 2012 |
| Classic Roofers Ltd | Construction | 2024 |
| Classy Dosky Ltd | Other services | 2025 |
| Clatworthy Management Ltd | Professional & scientific | 2014 |
| Claude Mark Ltd | Information & communication | 2026 |
| Claws, Wings and Other Things Limited | Administrative & support | 2016 |
| Clay Corporation Limited | Financial services | 2025 |
| Claybank Car Sales Ltd | Wholesale & retail | 2021 |
| Clayma Support and Child Services Ltd | Health & social care | 2022 |
| Claystone Homes Ltd | Real estate | 2019 |
| Clclj Ltd | Administrative & support | 2025 |
| Clean & Clear Southern Ltd | Water & waste | 2019 |
| Clean and Shiny Hand Car Wash Ltd | Administrative & support | 2026 |
| Clean Portsmouth Limited | Administrative & support | 2018 |
| Clean Teeth Staffing Ltd | Transport & logistics | 2021 |
| Cleaner Cars Ltd | Administrative & support | 2008 |
| CLEANSE2U Imre Tanko | | 2009 |
| Clear Contracting Solutions Limited | Construction | 2025 |
| Clear Figures Ltd | Professional & scientific | 2011 |
| Clear Star Investment Limited | Hospitality | 2021 |
| Clear Vision Window Cleaning Ltd | Administrative & support | 2015 |
| Clearnest Cleaning Services Ltd | Administrative & support | 2025 |
| Clearstream Property Limited | Real estate | 2016 |
| Clearstyle UK Limited | Wholesale & retail | 2026 |
| Clearvital Social Care Ltd | Health & social care | 2025 |
| Clemineo Limited | Professional & scientific | 2014 |
| Cleveland Court (Southsea) Limited | Households | 2005 |
| CLG Counselling Limited | Financial services | 2021 |
| CLG SPV 001 Limited | Financial services | 2023 |
| CLH Healthcare LLP | | 2013 |
| Clicflux Limited | Professional & scientific | 2015 |
| Click & Pack Limited | Wholesale & retail | 2024 |
| Clientele Care Ltd | Administrative & support | 2024 |
| Climate Conditioning Services Ltd | Construction | 2020 |
| Climaur Properties (Southern) Limited | Construction | 1985 |
| Climaur Properties Limited | Construction | 1984 |
| Climbing Club Ltd | Arts & recreation | 2025 |
| Clinical Trial Partnerships Ltd | Professional & scientific | 2023 |
| Clivet Group UK Limited | Manufacturing | 2001 |