| Compound Freedom Limited | Information & communication | 2014 |
| Compound Semiconductor Centre Limited | Manufacturing | 2014 |
| Comprinno Technologies UK Limited | Information & communication | 2025 |
| Comprx Ltd | Wholesale & retail | 2015 |
| Compusolve International Limited | Information & communication | 1997 |
| Computational and Scientific Consultancy Services Ltd. | Professional & scientific | 2015 |
| Computer Giantz Limited | Wholesale & retail | 2021 |
| Computer Key Services Ltd | Other services | 2020 |
| Computer Trend UK Ltd | Other services | 2019 |
| Computerisation Limited | Information & communication | 1989 |
| Computerworld (Wales) Limited | Information & communication | 1992 |
| Computing Network Ltd | Information & communication | 2022 |
| Comrades Health Care Ltd | Other services | 2015 |
| Comtech Engineers Ltd. | Manufacturing | 2011 |
| Comudity Ltd | Wholesale & retail | 2025 |
| Comustafa Ltd | Wholesale & retail | 2023 |
| COMWAT-103 Limited Partnership | | 2018 |
| CON Amore Ltd | Other services | 2021 |
| Concentric Health Ltd | Health & social care | 2017 |
| Concept 6 Management Company Ltd | Financial services | 2022 |
| Concept Audiology Clinic Ltd | Wholesale & retail | 2025 |
| Concept Construction and Groundworks Limited | Construction | 2020 |
| Concept DL Limited | Information & communication | 2004 |
| Concept EYE Perivale Ltd | Wholesale & retail | 2024 |
| Concept Fire and Security Solutions Limited | Administrative & support | 2014 |
| Concept Fire Protection Limited | Public administration | 2022 |
| Concept Fire Sprinklers Limited | Administrative & support | 2014 |
| Concept Property Solutions Ltd | Construction | 2019 |
| Concept Q Ltd | Wholesale & retail | 2010 |
| Concept Rugs Ltd | Manufacturing | 2018 |
| Concept Sunbeds Limited | Other services | 2015 |
| Concept-Finesse Projects Ltd | Other services | 2018 |
| CONCEPT22 Group Ltd | Wholesale & retail | 2016 |
| Concepta Diagnostics Limited | Health & social care | 2025 |
| Conceptivise Ltd | Information & communication | 2025 |
| Concierge Health London Limited | Health & social care | 2024 |
| Concilium Life Sciences Ltd | Administrative & support | 2024 |
| Concilium Search Limited | Administrative & support | 2014 |
| Concilium Search Sports Ltd | Administrative & support | 2022 |
| Conciptual Ltd | Wholesale & retail | 2018 |
| Concire Ltd | Construction | 2025 |
| Conclusio Ltd | Professional & scientific | 2014 |
| Concord Security Solutions Limited | Administrative & support | 2013 |
| Concorde Hub Ltd | Real estate | 2024 |
| Concordia Forge Limited | Professional & scientific | 2025 |
| Concrete Box Limited | Professional & scientific | 2024 |
| Concrete Pump London Limited | Administrative & support | 2017 |
| Condenser Consultancy Services Limited | Professional & scientific | 2002 |
| Cone Monkey Ltd | Other services | 2019 |
| Conelab Ltd | Hospitality | 2023 |
| Coneli Ltd | Wholesale & retail | 2019 |
| Conexom Ltd | Information & communication | 2021 |
| Conexus DX Limited | Administrative & support | 2019 |
| Confictura Ltd | Construction | 2023 |
| Configurable Solutions Ltd | Professional & scientific | 2009 |
| Conflict Resolutions Training & Consultancy Limited | Education | 2017 |
| Conform Fire & Security Ltd | Administrative & support | 2019 |
| Conformity Plus Limited | Professional & scientific | 2021 |
| Confused.Com Limited | Professional & scientific | 1999 |
| Congaton Ltd | Manufacturing | 2024 |
| Congress Events Ltd | Administrative & support | 2019 |
| Conife Ltd | Wholesale & retail | 2020 |
| Conix Site Machining Ltd. | Professional & scientific | 1989 |
| Conjoined Destiny Limited | Administrative & support | 2025 |
| Conlast Nutrition Ltd | Wholesale & retail | 2024 |
| Conlivi | Professional & scientific | 2024 |
| Connaught House (Cardiff) Limited | Households | 1986 |
| Connaught House Roath 1 Limited | Administrative & support | 2016 |
| Connaught Mews Management Company Limited | Households | 1990 |
| Connaught Road Flat Management Limited | Households | 1991 |
| Connect & Create Vibez Ltd | Arts & recreation | 2022 |
| Connect and Flourish Coaching Ltd | Education | 2023 |
| Connect Assist Holdings Limited | Health & social care | 2017 |
| Connect Assist Limited | Health & social care | 2005 |
| Connect Electrical Installations Limited | Construction | 2012 |
| Connect Enterprises Limited | Real estate | 2020 |
| Connect HUT Ltd | Wholesale & retail | 2018 |
| Connect Language Services Ltd | Administrative & support | 2016 |
| Connect Transport Services Limited | Transport & logistics | 2017 |
| CONNECT201 Ltd | Information & communication | 2019 |
| Connected Backoffice Ltd | Administrative & support | 2016 |
| Connected Commercial Solutions Limited | Professional & scientific | 2018 |
| Connected Finance Partner Ltd | Professional & scientific | 2017 |
| Connective Care Education Ltd | Health & social care | 2009 |
| Connectx Ltd | Other services | 2017 |
| Connelbuild Ltd | Construction | 2022 |
| Connell Legal Limited | Professional & scientific | 2015 |
| Conner Ltd | Construction | 2014 |
| Connex Network Management Ltd | Construction | 2024 |
| Connex Network Management Solutions Ltd | Transport & logistics | 2026 |
| Connexion Stewardship Ltd | Real estate | 2025 |
| Connies of Cardiff Limited | Construction | 1926 |
| Cono Ariti Consulting Limited | Professional & scientific | 2025 |
| Conor Patrick Ltd | Information & communication | 2023 |
| Conquerant Vainqueur Ltd | Other services | 2025 |
| Conquerneering Ltd | Manufacturing | 2018 |
| Conqueror Landscaping Contractors Ltd | Administrative & support | 2025 |
| Conquest Guarding Limited | Transport & logistics | 2018 |
| Conrad Stone CYF | Information & communication | 2022 |
| Conradier Ltd | Wholesale & retail | 2025 |