| Capital City Service Limited | Information & communication | 2003 |
| Capital Connect Property Ltd | Real estate | 2024 |
| Capital Construction Company (London) Limited | Construction | 2015 |
| Capital Creek Ltd | Real estate | 2024 |
| Capital Exim LP | | 2017 |
| Capital Group London Limited | Financial services | 2015 |
| Capital Interim Limited | Construction | 2012 |
| Capital Property Sourcers Ltd | Professional & scientific | 2020 |
| Capital Sanding Ltd | Construction | 2023 |
| Capital Services (Watford) Limited | Construction | 2000 |
| Capital Services Corporation Limited | Wholesale & retail | 2006 |
| Capital Services Watford (Holdco) Limited | Financial services | 2024 |
| Capital Shopfitters Limited | Construction | 2002 |
| Capital Tyres Watford Ltd | Wholesale & retail | 2024 |
| CAPITAL36 CTV2 Limited | Real estate | 2025 |
| Capitis Consulting Limited | Extraterritorial | 2013 |
| Capitol Commercial Collections Limited | Financial services | 1998 |
| Capitol Developments Ltd | Real estate | 2021 |
| Capitol Enterprise Ltd | Real estate | 2019 |
| Capitol Holdings Ltd | Real estate | 2019 |
| Capitol Partners Ltd | Real estate | 2022 |
| Capitol Ventures Ltd | Real estate | 2023 |
| Capoprits Ltd | Information & communication | 2021 |
| Capper Engineering Services | Manufacturing | 1984 |
| Capsco Limited | Professional & scientific | 2020 |
| Capstone Realty Ltd | Real estate | 2019 |
| Capsule Whales Limited | Construction | 2024 |
| Capthorne Court Limited | Real estate | 1996 |
| Capthorne Court RTM Company Limited | Real estate | 2012 |
| Capvent Limited | Real estate | 2018 |
| Car Care Club Ltd | Administrative & support | 2026 |
| Car Nect Ltd | Construction | 2019 |
| Car Souk Ltd | Wholesale & retail | 2025 |
| Car Tier S Ltd | Transport & logistics | 2025 |
| Carbon Rewind Holdings Limited | Financial services | 2021 |
| Carbon Rewind Insulation Ltd | Construction | 2021 |
| Carbon Rewind Ltd | Construction | 2019 |
| Carbon Rewind Renewables Ltd | Construction | 2021 |
| Carbonyte Limited | Professional & scientific | 2020 |
| Cardell Property Services Ltd | Real estate | 2015 |
| Cardiac Care London Limited | Health & social care | 2023 |
| CARDS2LANKA UK Ltd | Wholesale & retail | 2020 |
| Care 4 Herts Ltd | Other services | 2017 |
| Care About US Ltd | Health & social care | 2022 |
| Care at Heart Ltd | Health & social care | 2022 |
| Care Force Uniform Limited | Manufacturing | 2006 |
| Care Full Care Limited | Public administration | 2019 |
| Care Home Services Limited | Health & social care | 2016 |
| Care Oasis Homes Ltd | Health & social care | 2024 |
| Care Plus Recruitment Agency Limited | Health & social care | 2016 |
| Care RES Ltd | Real estate | 2024 |
| CARE2BUILD Ltd | Construction | 2018 |
| Carebuild Ltd | Administrative & support | 2025 |
| Carecircle Healthcare Ltd | Administrative & support | 2016 |
| Careclean Solutions Limited | Administrative & support | 2025 |
| Career Artist Ltd | Professional & scientific | 2014 |
| Career Cocoon Ltd | Extraterritorial | 2012 |
| Career Transitions Hub Ltd | Other services | 2025 |
| Carenavo Ltd | Information & communication | 2026 |
| Carers in Your Home Ltd | Professional & scientific | 2012 |
| Carew Road Residents Association Limited | Households | 1988 |
| Careway Domicilliary Limited | Health & social care | 2026 |
| Cargo Gateway Limited | Transport & logistics | 2003 |
| Cargonex Ltd | Transport & logistics | 2024 |
| Caribou Poutine Ltd | Administrative & support | 2016 |
| Caring Hands and Care Solutions Group Limited | Health & social care | 2026 |
| Carisma Family Investment Company Limited | Real estate | 2022 |
| Carl Technology Ltd | Information & communication | 2022 |
| Carlo Cheesesteaks Limited | Hospitality | 2024 |
| Carlos Gardener Ltd | Other services | 2023 |
| Carlton Contractors Limited | Professional & scientific | 1939 |
| Carly Cook Ltd | Professional & scientific | 2023 |
| Carmel Property Limited | Real estate | 2019 |
| Carmel Treanor Limited | Health & social care | 2015 |
| Carmody Solutions Limited | Professional & scientific | 2025 |
| Carmoon Investment Ltd | Real estate | 2022 |
| Carne Family Ltd | Professional & scientific | 2022 |
| Carocar Ltd | Construction | 2020 |
| Caroline Lodge Management Company Limited | Real estate | 1998 |
| Carols Latin Jive Limited | Arts & recreation | 2011 |
| Carpenders Park and South Oxhey Labour Hall Limited | Real estate | 2025 |
| Carpenders Park Community Hall Association Limited | Real estate | 1990 |
| Carpentry Cornwall Ltd | Construction | 2021 |
| Carpet Works Ltd | Wholesale & retail | 2024 |
| Carrico Gardening Ltd | Administrative & support | 2019 |
| Carrier Connect Logistics Limited | Transport & logistics | 2025 |
| Carringtons Global Limited | Real estate | 2011 |
| Carroll Electrical Installations Limited | Construction | 2015 |
| Carsola Ltd | Administrative & support | 2015 |
| Cartridge Works Watford Ltd | Wholesale & retail | 2021 |
| Casa Bianca Ltd | Real estate | 2021 |
| Casa Colombia UK C.I.C. | Administrative & support | 2024 |
| Casa DE Grace Ltd | Real estate | 2023 |
| Casa EL Pastor Limited | Hospitality | 2017 |
| Casa Maid (UK) Ltd | Administrative & support | 2015 |
| Casa Nostra Household Recruitment Limited | Administrative & support | 2025 |
| Casa Nova London Limited | Real estate | 2013 |
| Casa Nova Property Investments Limited | Real estate | 2013 |
| Casa PAN Asian Food Ltd | Hospitality | 2026 |
| Casanova UK Investments Limited | Real estate | 2015 |