| Cleveland Properties Limited | Professional & scientific | 1913 |
| Cleveland Steels Ltd | Manufacturing | 2012 |
| Cleveland Wealth Management Ltd | Financial services | 2016 |
| Click Hire Ltd | Transport & logistics | 2025 |
| Click in Energy Services Ltd | Information & communication | 2025 |
| Cliff Court (Redcar) Developments Ltd | Real estate | 2010 |
| Cliffe Renewable Services Ltd | Administrative & support | 2022 |
| Cliffl Limited | Professional & scientific | 2020 |
| Climate Change Technologies Limited | Professional & scientific | 2004 |
| Climb & Conquer Ltd | Professional & scientific | 2021 |
| Clinical PPE Ltd | Wholesale & retail | 2020 |
| Clock Emporium Limited | Wholesale & retail | 2014 |
| Close Protection Security NE Ltd | Administrative & support | 2026 |
| Cloud Engagement Limited | Professional & scientific | 2014 |
| Cloudconcur Ltd | Information & communication | 2021 |
| Clover & Co Florist Limited | Wholesale & retail | 2024 |
| CLS Property Management Limited | Households | 2021 |
| CLS Tubing Limited | Construction | 2017 |
| Club North East Ltd | Transport & logistics | 2019 |
| CM Health Consultancy Ltd | Professional & scientific | 2024 |
| CM Operations and Management Ltd | Administrative & support | 2011 |
| CM Worldwide Inspection Services Ltd | Administrative & support | 2024 |
| CMC Access and Coatings Limited | Construction | 2015 |
| CMC Cafe Lounge Limited | Hospitality | 2012 |
| CMH Auto's Ltd | Wholesale & retail | 2021 |
| CML Products Limited | Professional & scientific | 2014 |
| CMR Mechanical Services Ltd | Manufacturing | 2020 |
| CMT Medical Services Limited | Health & social care | 2020 |
| Cniw Capital Ltd | Professional & scientific | 2019 |
| Cniw Dwallet Ltd | Financial services | 2019 |
| Cniw European Global Ltd | Extraterritorial | 2019 |
| Cniw Fidelity Global Ltd | Information & communication | 2006 |
| Cniw Fincorp Limited | Professional & scientific | 2025 |
| Cniw Meana Global Ltd | Professional & scientific | 2007 |
| Cniw PLC | Administrative & support | 2022 |
| Cniw Securities Ltd | Financial services | 2022 |
| Cniw Sovereign Global Ltd | Other services | 2017 |
| Cniw Wealth Management Limited | Financial services | 2024 |
| Co. Durham Land LLP | | 2018 |
| Coachedbyct Ltd | Health & social care | 2025 |
| Coalescence Health Ltd | Health & social care | 2024 |
| Coan Properties Ltd | Real estate | 2025 |
| Coast Gate Ltd | Financial services | 2021 |
| Coatham Care Solutions Limited | Health & social care | 2025 |
| Coatham Stob Agricultural Fencing Ltd | Construction | 2023 |
| Cockerton Green Developments Ltd | Real estate | 2009 |
| Coconut Agency Ltd | Administrative & support | 2022 |
| Coconut Group Ltd | Financial services | 2023 |
| Codepitcher Ltd | Information & communication | 2012 |
| Codsawyu Ltd | Wholesale & retail | 2025 |
| Coffeeandteesco Ltd | Hospitality | 2023 |
| Coils by Scott Ltd | Wholesale & retail | 2023 |
| Coleman and Hugill Ltd | Hospitality | 2026 |
| Colewood Automotive Limited | Wholesale & retail | 2017 |
| Colewood Collaborations Ltd | Wholesale & retail | 2022 |
| Colin Trotter Builders Ltd | Construction | 2024 |
| Collab Media Limited | Professional & scientific | 2021 |
| Colour Index Decorating Limited | Construction | 2008 |
| Colvin Quality Consulting Ltd | Professional & scientific | 2016 |
| Comfort in Luxury Ltd | Wholesale & retail | 2025 |
| Comfy Canines Ltd | Households | 2019 |
| Commercial Interiors Stockton Ltd | Construction | 2011 |
| Commplex Group Ltd | Other services | 2021 |
| Commplex Hire Services Limited | Administrative & support | 2021 |
| Commplex Network Services Ltd | Other services | 2017 |
| Commplex Utility Services Limited | Construction | 2021 |
| Community Issues and Concerns (Ci&C) CIC | Information & communication | 2022 |
| Community Projects (North East) CIC | Health & social care | 2023 |
| Compass Brickwork Contractors Ltd | Construction | 2019 |
| Compass People Solutions Ltd | Administrative & support | 2025 |
| Compcrest Limited | Professional & scientific | 1996 |
| Competency EX Ltd | Education | 2025 |
| Compilation Group Limited | Manufacturing | 2023 |
| Complete Core Ltd | Wholesale & retail | 2021 |
| Complete Legal Limited | Professional & scientific | 2025 |
| Complex Installations Ltd | Construction | 2025 |
| Complimate Group Limited | Professional & scientific | 2025 |
| Con-Force Developments Ltd | Real estate | 2025 |
| Con-Force UK Ltd | Professional & scientific | 2017 |
| Concentrated Solutions Limited | Administrative & support | 2006 |
| Confined Space Rescue Solutions Ltd | Professional & scientific | 2024 |
| Coniscliffe Brew Company Limited | Hospitality | 2022 |
| Connect Property North East Ltd | Real estate | 2015 |
| Connection First Speech and Language Therapy Ltd | Health & social care | 2026 |
| Connolly, Keiller and Whitburn Limited | Financial services | 1993 |
| Connor Brown Logistics Ltd | Transport & logistics | 2025 |
| Conor Holdings Limited | Real estate | 2021 |
| Consequi Limited | Professional & scientific | 2015 |
| Conservatory Blinds Direct Ltd | Manufacturing | 2015 |
| Consoli Limited | Information & communication | 2010 |
| Constantine Media Ltd | Manufacturing | 2021 |
| Construction Recruitment 24HRS Ltd | Administrative & support | 2023 |
| Construction Skills Development Ltd | Education | 2024 |
| Consultants Choice Clinic Ltd | Administrative & support | 2024 |
| Container Container Ltd | Administrative & support | 2008 |
| Contract Connections Limited | Administrative & support | 1997 |
| Contract Natural GAS (Marketing) Limited | Wholesale & retail | 1997 |
| Conveyors Direct Online Ltd | Manufacturing | 2007 |
| Cook Construction Contract Consultancy Limited | Professional & scientific | 2013 |
| Cookie JAR Collectables Ltd | Wholesale & retail | 2025 |