| Collegia Partners Trustees Limited | Financial services | 2019 |
| Colman & Co Estate Agents Ltd | Real estate | 2016 |
| Colour Vibes Limited | Professional & scientific | 2018 |
| Colourful Coffins Limited | Extraterritorial | 2008 |
| Colourkind Ltd | Wholesale & retail | 2020 |
| Colourview Print Solutions Ltd | Manufacturing | 2024 |
| Colthorn Farm Management Company Limited | Households | 2019 |
| Comfort Trust | Education | 2006 |
| Comicebooks Limited | Information & communication | 2012 |
| Comie's Caribbean Grill Ltd. | Hospitality | 2015 |
| Commerce Accel Limited | Professional & scientific | 2020 |
| Commercial Communications Group Limited | Professional & scientific | 1999 |
| Commercial Communications Limited | Professional & scientific | 1999 |
| Commercial Finance Specialists Limited | Financial services | 2016 |
| Commercial ROW Limited | Real estate | 2007 |
| Common Ground Oxford Ltd | Hospitality | 2026 |
| Comms Design Limited | Professional & scientific | 2004 |
| Communications Chambers RK Ltd | Professional & scientific | 2010 |
| Community Acupuncture Team CIC | Health & social care | 2020 |
| Community Based Mindfulness C.I.C. | Health & social care | 2019 |
| Community Catch Ltd | Professional & scientific | 2022 |
| Community Environment Associates Limited | Professional & scientific | 2006 |
| Community Glue C.I.C. | Health & social care | 2010 |
| Companion Cardiology Limited | Professional & scientific | 2026 |
| Companions for Leadership Limited | Professional & scientific | 2016 |
| Comparethesupermarket Ltd | Information & communication | 2024 |
| Compass 8 Limited | Professional & scientific | 2018 |
| Compassion in Action Oxford Ltd | Health & social care | 2015 |
| Compassionate Care Oxford Ltd | Health & social care | 2025 |
| Competent Creations Ltd | Information & communication | 2023 |
| Complete EV Solutions Limited | Construction | 2021 |
| Complete Gcse Ltd | Education | 2023 |
| Complete Physiotherapy Limited | Health & social care | 2007 |
| Complete Tree Services (UK) Limited | Agriculture & fishing | 2001 |
| Complex KYC Solutions Limited | Professional & scientific | 2018 |
| Compliance Sync Limited | Information & communication | 2026 |
| Complimenti Fashions Limited | Other services | 1979 |
| Compton Terrace Estates Limited | Extraterritorial | 2007 |
| Compton Terrace Limited | Extraterritorial | 2007 |
| Compton Terrace Properties Limited | Extraterritorial | 2007 |
| Compuhub Ltd | Information & communication | 2017 |
| Computercraft Data Systems Limited | Professional & scientific | 1997 |
| Computers and Games Ltd | Wholesale & retail | 2026 |
| Concept Healthcare Limited | Wholesale & retail | 2017 |
| Concerca Limited | Information & communication | 2010 |
| Concordia Spires Limited | Other services | 2006 |
| Connect 195 Ltd | Information & communication | 2021 |
| Connect Schools Limited | Education | 2020 |
| Connectingdoorz Limited | Financial services | 2024 |
| Connection Support | Health & social care | 1995 |
| Connectomx Ltd | Professional & scientific | 2017 |
| Connectus Solutions Limited | Other services | 2026 |
| Connex Technologies Ltd | Wholesale & retail | 2007 |
| Conolgrey Limited | Administrative & support | 2012 |
| Conquanto Ltd | Professional & scientific | 2024 |
| Conquistadores (CQD) LLP | | 2017 |
| Conscious Mata Consulting Ltd | Professional & scientific | 2025 |
| Conservation Education & Research Trust | Professional & scientific | 2002 |
| Conservation Investment Company Ltd | Financial services | 2025 |
| Constant Sandwiches Limited | Hospitality | 2024 |
| Construct Oxford Ltd | Administrative & support | 2025 |
| Construction Xhaferaj Ltd | Construction | 2021 |
| Consult HB Limited | Professional & scientific | 2013 |
| Consult NO 10 Ltd | Professional & scientific | 2012 |
| Consult Sync Solutions Limited | Information & communication | 2023 |
| Consultant Connect Limited | Information & communication | 2015 |
| Consultant GP Ltd | Health & social care | 2025 |
| Consultist Limited | Wholesale & retail | 2003 |
| Consume Talent Ltd | Administrative & support | 2015 |
| Contained Creatives Limited | Arts & recreation | 2019 |
| Contemporary Review Company,Limited(The) | Information & communication | 1891 |
| Continuum Chiropractic Limited | Health & social care | 2021 |
| Contour Interiors Ltd | Construction | 2025 |
| Contract Furniture (Oxford) Ltd | Wholesale & retail | 2022 |
| Contrada Limited | Information & communication | 2008 |
| Control Lighting Limited | Construction | 2004 |
| Convert My Conservatory Ltd | Construction | 2019 |
| Convolution AI Ltd | Professional & scientific | 2022 |
| Conway & Partners Ltd | Professional & scientific | 2022 |
| Conzense Ltd | Information & communication | 2018 |
| Cook EAT Discover LLP | | 2024 |
| Cool Escapes Limited | Real estate | 2020 |
| Cool Loong Hobby Ltd | Wholesale & retail | 2025 |
| Cool Places Limited | Information & communication | 2011 |
| Coolbyte Limited | Professional & scientific | 1987 |
| Cooli Finance Ltd | Financial services | 2025 |
| Coombe Castle Fine Wines Limited | Wholesale & retail | 1985 |
| Coombe Investments Limited | Real estate | 1960 |
| Cooper & Franklin Limited | Construction | 2007 |
| Cooper Brown Consulting Limited | Information & communication | 2026 |
| Coopers Property Holdings Limited | Real estate | 1997 |
| Coorig Ltd | Real estate | 2017 |
| Copping Engineering Solutions Limited | Professional & scientific | 2011 |
| Corcoran Homes Limited | Construction | 2003 |
| Cordis ET Sanguinis Limited | Professional & scientific | 2018 |
| Core Economics Education | Education | 2016 |
| Core Evolution Limited | Health & social care | 2013 |
| Core Ideas Ltd | Professional & scientific | 2024 |
| Core Unit Limited | Professional & scientific | 2020 |
| Corefiling Employee Benefits Limited | Extraterritorial | 2008 |