| Church Finance Supplies Limited | Manufacturing | 1967 |
| Church Lane Dental Practice Limited | Health & social care | 2010 |
| CIL 5 Ltd | Transport & logistics | 2022 |
| Cipher IT Services Limited | Information & communication | 2005 |
| Circa Projects Ltd | Real estate | 2025 |
| Circle Performance Ltd | Manufacturing | 2025 |
| Citara Holdings Limited | Financial services | 2024 |
| City & County Graphics Limited | Manufacturing | 2009 |
| City & County Signs Limited | Extraterritorial | 2015 |
| City Scaffolding Services Limited | | 1991 |
| Civil Nuclear Constabulary Welfare Limited | Other services | 2010 |
| CJA Limited | Real estate | 2009 |
| Cjmh Limited | Construction | 2015 |
| CK Conveyancing Ltd | Professional & scientific | 2021 |
| CK Warren Ltd | Professional & scientific | 2026 |
| Clare Painter Associates Ltd | Information & communication | 2009 |
| Clare Properties Limited | Real estate | 1962 |
| Claresys Limited | Manufacturing | 2008 |
| Claret (NT) Limited | Professional & scientific | 2013 |
| Clargo Outdoors Limited | Arts & recreation | 2026 |
| Clark Widdowson Enterprises Ltd | Wholesale & retail | 2021 |
| Clayton Stables Ltd | Arts & recreation | 2024 |
| Cleal’S Wheels Ltd | Education | 2025 |
| Clean Oasis Ltd | Administrative & support | 2016 |
| Clean Oasis Services Ltd | Administrative & support | 2022 |
| Cleaner Difference Team Oxford Limited | Other services | 2015 |
| Cleaning and Laundry Services Ltd | Hospitality | 2018 |
| Cleaning O'Clock Ltd | Administrative & support | 2014 |
| Clear Skies Interactive Ltd | Information & communication | 2025 |
| Clear Sky Children's Charity | Education | 2010 |
| Clearwater Gifts Limited | Wholesale & retail | 2012 |
| Clearwater Hampers Limited | Wholesale & retail | 2007 |
| Clearwater Hampers Operations Limited | Wholesale & retail | 2008 |
| Cleary Bros Ltd | Households | 2024 |
| Clerbise 15 Limited | Health & social care | 2016 |
| Clerbise Property Holdings Limited | Real estate | 2021 |
| Click to Deliver Ltd | Wholesale & retail | 2022 |
| Climate Outreach | Professional & scientific | 2007 |
| Close END Drayton Management Limited | Households | 2018 |
| Cloud Sham Ltd | Health & social care | 2016 |
| Cloud Studios TWB Ltd | Arts & recreation | 2026 |
| Cloudbase Ventures Ltd | Professional & scientific | 2021 |
| Cloudify 247 Ltd | Wholesale & retail | 2026 |
| Club Barber Abingdon Ltd | Wholesale & retail | 2026 |
| Clubb Private Endeavour (UK) Limited | Extraterritorial | 2022 |
| Cmpcon Ltd | Information & communication | 2012 |
| CMS Ergonomics Limited | Extraterritorial | 1997 |
| CMS Industries Limited | Wholesale & retail | 1990 |
| CMW Properties Limited | Real estate | 2017 |
| CO2OLTEC Commercial Refrigeration UK Limited | Other services | 1968 |
| Coach YOU Ltd | Education | 2007 |
| Cobalt Creative Limited | Administrative & support | 2008 |
| Cobe Property Ltd | Construction | 2018 |
| Cockpit Consultancy Ltd | Information & communication | 2020 |
| Codegate Limited | Information & communication | 1990 |
| Cognetra Solutions Ltd | Information & communication | 2025 |
| Cognitive Analytic Therapy Oxfordshire Ltd | Health & social care | 2020 |
| Coldfrontt Ltd | Wholesale & retail | 2024 |
| Colin Pink Sound Design Limited | Arts & recreation | 2018 |
| Collective Minds Ltd | Professional & scientific | 2020 |
| Collington Consultancy Limited | Information & communication | 2024 |
| Combe Capital Limited | Financial services | 2026 |
| Combe Holdings Limited | Financial services | 2026 |
| Combe Productions Limited | Arts & recreation | 2012 |
| Comd Limited | Wholesale & retail | 2017 |
| COMI360 Ltd | Wholesale & retail | 2025 |
| Commercial and Domestic Heat Pumps Ltd | Construction | 2025 |
| Common Barn Wind Farm Ltd | Energy | 2012 |
| Compactstream Limited | Information & communication | 1992 |
| Complete Home and Garden Care Ltd | Administrative & support | 2012 |
| Comprop Oxford Limited | Real estate | 2014 |
| Comtrex Systems Corporation Limited | Manufacturing | 1978 |
| Conatus London Limited | Manufacturing | 2021 |
| Concordia Solutions Limited | Professional & scientific | 2006 |
| Concrete Thoughts Limited | Professional & scientific | 2020 |
| Conkers Wood and Metal Crafts Ltd | Manufacturing | 2021 |
| Connect Properties Limited | Real estate | 1997 |
| Connecting the Culture Limited | Professional & scientific | 2020 |
| Connection Conduit Limited | Information & communication | 2022 |
| Connection Vibrant Limited | Information & communication | 2018 |
| Conrad (2022) Limited | Energy | 2020 |
| Conrad (Alcoa) Limited | Energy | 2020 |
| Conrad (Ampthill) Limited | Energy | 2017 |
| Conrad (Arncott) Limited | Energy | 2018 |
| Conrad (Aurelius) Holdco Limited | Financial services | 2023 |
| Conrad (Aurelius) Limited | Financial services | 2023 |
| Conrad (Barton Hill) Limited | Energy | 2020 |
| Conrad (Basingstoke) Limited | Administrative & support | 2020 |
| Conrad (Beighton) Limited | Energy | 2021 |
| Conrad (Belton Farm) Limited | Energy | 2025 |
| Conrad (Benfleet) Limited | Energy | 2016 |
| Conrad (Billericay) Limited | Energy | 2020 |
| Conrad (Bilsham) Limited | Energy | 2022 |
| Conrad (Bilston) Limited | Energy | 2018 |
| Conrad (Bishopstoke) Limited | Energy | 2022 |
| Conrad (Bispham) Limited | Energy | 2016 |
| Conrad (Blackpool) Limited | Energy | 2020 |
| Conrad (Bletchley) Limited | Energy | 2015 |
| Conrad (Bolton a) Limited | Energy | 2023 |
| Conrad (Bolton B) Limited | Energy | 2023 |