| Bulb Marketing Limited | Information & communication | 2018 |
| Bulk Materials Ltd | Transport & logistics | 2020 |
| Bulldog Branding Limited | Wholesale & retail | 2021 |
| Burrowfield Auto Services Limited | Wholesale & retail | 1994 |
| Burrowfield Hand Car Wash Ltd | Other services | 2015 |
| Bury Sublettings Ltd | Real estate | 2024 |
| Bushey LEY Property Ltd | Real estate | 2025 |
| Buttoncase Limited | Administrative & support | 2004 |
| BWR Media Limited | Arts & recreation | 2014 |
| Bwssk Consult Ltd | Real estate | 2021 |
| Byosys Limited | Information & communication | 2010 |
| Bytehouse Limited | Extraterritorial | 2008 |
| C Builders Ltd | Construction | 2014 |
| C&I Housing Management Ltd | Real estate | 2025 |
| C&Z Kitchen Limited | Manufacturing | 2024 |
| C.A.Head Ltd | Construction | 2025 |
| C.G. Edward (Goffs Oak) Limited | Administrative & support | 1964 |
| C.J. Honan Ceramics Ltd | Construction | 2023 |
| C.Phillips Roofing Ltd | Construction | 2021 |
| C.W. Housing Solutions Ltd | Real estate | 2024 |
| CA Creative Services Ltd | Professional & scientific | 2024 |
| Calington Limited | Wholesale & retail | 2003 |
| Cally Care Ltd | Public administration | 2022 |
| Calvary School of Prophetic Ministry Ltd | Education | 2009 |
| Camellia Construction Limited | Construction | 2024 |
| Camloc Ltd | Real estate | 2016 |
| Camoys Properties Ltd | Real estate | 2018 |
| Campbell Reed Limited | Administrative & support | 2015 |
| Cannstatt Ltd | Wholesale & retail | 2020 |
| Canonsfield Court Residents Association Limited | Households | 1978 |
| Canopy Great Amwell Ltd | Education | 2026 |
| Cansu Sahin Ltd | Information & communication | 2024 |
| CAP Film Solutions Ltd | Administrative & support | 2025 |
| Capacitex Limited | Information & communication | 2011 |
| Capital Plant Solutions (GB) Ltd | Construction | 2011 |
| Capparoy Properties Ltd | Real estate | 2026 |
| Car Genie Repairs Ltd | Wholesale & retail | 2025 |
| Care for Excellence Limited | Health & social care | 2025 |
| Care Herts Limited | Health & social care | 2013 |
| Care on Call Health Care Ltd | Health & social care | 2025 |
| Caredrop Ltd | Transport & logistics | 2025 |
| CAREE4U Limited | Health & social care | 2022 |
| Careernature Limited | Education | 1994 |
| Carequest Staffing Limited | Administrative & support | 2026 |
| Carers Worldwide | Public administration | 2012 |
| Carl Fitzpatrick Associates Limited | Construction | 2013 |
| Carrick Machinery Ltd | Wholesale & retail | 2025 |
| Cartech Welwyn Ltd | Wholesale & retail | 2016 |
| Cartridge King Limited | Wholesale & retail | 2021 |
| Carvisor Ltd | Wholesale & retail | 2026 |
| Cashco Store Ltd | Wholesale & retail | 2020 |
| Cashluxe UK Ltd | Administrative & support | 2025 |
| Cassana Performance Academy Ltd | Education | 2018 |
| Castle Heating Herts Ltd | Construction | 2018 |
| Castlecrew Glazing Limited | Construction | 2023 |
| Catalin Ltd | Transport & logistics | 2019 |
| Catalyst Network International CIC | Other services | 2023 |
| CBM Group Ltd | Construction | 2013 |
| CC Publishing Ltd | Information & communication | 2019 |
| CC Sports Medicine Limited | Financial services | 2010 |
| Ccla (Luton) Limited | Construction | 2017 |
| CD Parents Hub Ltd | Education | 2025 |
| CDI Drylining Limited | Construction | 2022 |
| CDP Plastering Ltd | Construction | 2017 |
| Cedarmire Limited | Information & communication | 2018 |
| Cellome Ltd | Professional & scientific | 2025 |
| Cemaitech Limited | Professional & scientific | 2024 |
| Cereal Partners U.K. Pension Trust Limited | Financial services | 1976 |
| Ceres Security Limited | Administrative & support | 2019 |
| Cerro Ltd | Information & communication | 2020 |
| Cesar's Hygiene Limited | Professional & scientific | 2014 |
| Cfirst Background Checks Limited | Information & communication | 2022 |
| CGO Group Ltd | Financial services | 2026 |
| Chacha Global Ltd | Manufacturing | 2023 |
| Chadha Oriental Foods Limited | Wholesale & retail | 1980 |
| Chal Property Limited | Real estate | 2016 |
| Champagne Fashions Limited | Wholesale & retail | 1993 |
| Chancegate Limited | Other services | 2011 |
| Chapman (Welwyn) Limited | Administrative & support | 2017 |
| Chapman Ventilation Group Limited | Administrative & support | 2017 |
| Chapman Ventilation Holdings Ltd | Financial services | 2021 |
| Chapman Ventilation Limited | Construction | 2007 |
| Chapman Welwyn Holdings Ltd | Financial services | 2021 |
| Charge AC Ltd | Construction | 2019 |
| Charles of the Ritz Limited | Administrative & support | 2007 |
| Charlotte Zdybel Designs Limited | Arts & recreation | 2011 |
| Charm DE Vera Ltd | Wholesale & retail | 2026 |
| Chase (Ashwell) Limited | Construction | 2022 |
| Chase (Barnet) Limited | Construction | 2016 |
| Chase (Canada) Limited | Construction | 2025 |
| Chase (Cassio) Limited | Construction | 2015 |
| Chase (Cockfosters) Holding Limited | Construction | 2020 |
| Chase (Cockfosters) Limited | Construction | 2019 |
| Chase (Cuffley) Limited | Construction | 2017 |
| Chase (Hertford) Limited | Construction | 2019 |
| Chase (Herts) Limited | Construction | 2019 |
| Chase (Rickmansworth) Limited | Construction | 2014 |
| Chase (SW) Limited | Construction | 2018 |
| Chase (WGC) Limited | Construction | 2013 |
| Chase Broxbourne Limited | Construction | 2019 |