| Claudia Lovelady Interiors Ltd | Professional & scientific | 2021 |
| Clavus Capital Limited | Real estate | 1998 |
| Clay Cross Asset Management Ltd | Financial services | 2014 |
| Clean Genie Milton Keynes Ltd | Administrative & support | 2023 |
| Clean Loyal Solutions Oxford Ltd | Administrative & support | 2024 |
| Clean NET Service Limited | Administrative & support | 2023 |
| Clean World Specialist Limited | Administrative & support | 2019 |
| Cleanerstar GH Ltd | Administrative & support | 2026 |
| Cleaning Grace NA Ltd | Administrative & support | 2023 |
| Cleaning Oxford Ltd | Administrative & support | 2020 |
| Clear Brew High Wycombe and Swindon Ltd | Administrative & support | 2020 |
| Clearnest Pest Control Ltd | Administrative & support | 2025 |
| Clearpath IT Consulting Ltd | Information & communication | 2024 |
| Clearsky Group Holdings Limited | Manufacturing | 2025 |
| Clearwater (Oxford) Limited | Extraterritorial | 1999 |
| Cleaving Husband Foundation | Other services | 2026 |
| Clerkenwell EC1 Limited | Extraterritorial | 2007 |
| Clerkenwell Road Limited | Extraterritorial | 2007 |
| Clever Shopping Network Ltd | Wholesale & retail | 2025 |
| Clever Software Ltd | Information & communication | 2009 |
| Clevermed Limited | Information & communication | 1999 |
| Clicksavvy Store Ltd | Wholesale & retail | 2026 |
| Clientele Bureau ( CBL) Limited | Health & social care | 2015 |
| Cliff Estates Management Company Limited | Households | 2020 |
| Clifton Biomedical Consultants Ltd | Professional & scientific | 2020 |
| Climate Adapt Limited | Professional & scientific | 2010 |
| Climate Adaptation Learning LAB CIC | Professional & scientific | 2024 |
| Climate Tipping Point Ltd | Professional & scientific | 2021 |
| Clinic 95 Holdings (3) Limited | Financial services | 2024 |
| Clinic Escimo Ltd | Professional & scientific | 2021 |
| Clinical AI Partners Ltd. | Education | 2024 |
| Clinical Publishing Ltd | Information & communication | 2003 |
| Clinical Publishing Services Limited | Information & communication | 2000 |
| Clinops Specialists Limited | Professional & scientific | 2025 |
| Clinox Limited | Administrative & support | 2018 |
| Clive Smith (Oxford) Limited | Real estate | 1961 |
| Clive Woodward Building Services Limited | Construction | 2002 |
| Clmhg Limited | Other services | 2011 |
| Clock House Laboratories Ltd | Information & communication | 2025 |
| Clockwork-World Limited | Professional & scientific | 2013 |
| Cloud 10 Shisha Lounge Ltd | Administrative & support | 2017 |
| Cloud Controlled Limited | Information & communication | 2016 |
| Cloud Kickers Devices Limited | Professional & scientific | 2018 |
| Cloud Mortgage Services Limited | Financial services | 2018 |
| Cloud Your Business Limited | Information & communication | 2018 |
| CLOUD4RONT Ltd | Information & communication | 2024 |
| Cloudapps Ltd | Information & communication | 2009 |
| Cloudclinic Limited | Information & communication | 2013 |
| Cloudframes Ltd | Wholesale & retail | 2025 |
| Clouds Cafe Oxford Ltd | Hospitality | 2024 |
| Cloudy Bay Investments LLP | | 2006 |
| Clover Property Ltd | Real estate | 2022 |
| Clovers of Berinsfield Ltd | Wholesale & retail | 2011 |
| Cloverturn Limited | Professional & scientific | 2002 |
| CLS Energy (Consultancy) Limited | Professional & scientific | 2014 |
| Cluster Oxford Limited | Real estate | 2024 |
| Clyc Ltd | Manufacturing | 2023 |
| CM (Great Missenden) Ltd | Construction | 2023 |
| CMK Associates Ltd | Other services | 2021 |
| CMS House Enterprises Ltd | Real estate | 2015 |
| Co Mersey Holdco Limited | Financial services | 2025 |
| Co-Design Consulting Limited | Professional & scientific | 2008 |
| CO2ECO Limited | Professional & scientific | 2020 |
| Co:Cubed Limited | Information & communication | 2017 |
| Coach & BUS Week Limited | Information & communication | 2012 |
| Coach Carbon Ltd | Arts & recreation | 2021 |
| Coach LEX 1:1 Ltd | Education | 2018 |
| Coaching Oxford Limited | Professional & scientific | 2011 |
| Cobbold Medical Ltd | Health & social care | 2015 |
| Coco Factory Ltd | Information & communication | 2024 |
| Cocoon Design Limited | Arts & recreation | 2011 |
| Cocurricula LLP | | 2025 |
| Codamotion Ltd | Manufacturing | 1987 |
| Code Encryption Limited | Extraterritorial | 2013 |
| Code Magus Limited | Professional & scientific | 2000 |
| Coding BIO Limited | Professional & scientific | 2020 |
| Coelho Wilson Property Limited | Real estate | 2025 |
| Coffee With Nala Ltd | Hospitality | 2023 |
| Cogent Communication & Consulting Limited | Professional & scientific | 2011 |
| Coggleit Limited | Information & communication | 2014 |
| Cogneon Ltd | Health & social care | 2019 |
| Cognite Neurotechnology Limited | Professional & scientific | 2021 |
| Cognitio Systems Limited | Information & communication | 2010 |
| Cognitive Data Shop Ltd | Wholesale & retail | 2021 |
| Cognitive Data Systems Ltd | Information & communication | 2021 |
| Cognitive Therapy Oxford Limited | Education | 2010 |
| Cohen Kadosh Consultancy Limited | Professional & scientific | 2016 |
| Cohesion Developments Ltd | Construction | 2017 |
| Coils Property Ltd | Real estate | 2023 |
| Coinucopia Limited | Professional & scientific | 2016 |
| Colegrove Properties Limited | Financial services | 2017 |
| Coleman-Hilsdon Limited | Manufacturing | 2023 |
| Coleside Limited | Households | 2015 |
| Colhoq Developments Ltd | Real estate | 2025 |
| Collaborative Engineering Services Ltd | Professional & scientific | 2022 |
| Collections Marketing Centre UK Limited | Information & communication | 2008 |
| Collective Change Community Giving CIC | Other services | 2021 |
| College Flats Management Company Limited | Households | 1984 |
| College Press Ltd. | Information & communication | 2017 |
| Collegia Partners Limited | Information & communication | 2018 |