| Copper Beech Associates Limited | Information & communication | 2000 |
| Copra Limited | Other services | 2001 |
| Cord Health Consulting Ltd | Professional & scientific | 2021 |
| Coridian Media Ltd | Professional & scientific | 2024 |
| Cornish Communications Limited | Professional & scientific | 2018 |
| Cornish Pension Symphony Limited | Professional & scientific | 2022 |
| Corporate Payroll Solutions Limited | Information & communication | 1999 |
| Corporation Properties & Development Limited | Real estate | 2003 |
| Corry Motor Services Berkhamsted Limited | Wholesale & retail | 2026 |
| Corus Hotels Limited | Hospitality | 1920 |
| COS Design Ltd | Professional & scientific | 2023 |
| Cosyycorner Ltd | Wholesale & retail | 2021 |
| Cottonon Productions Limited | Information & communication | 2016 |
| Cougar Air Ltd. | Professional & scientific | 1988 |
| Cougar Industries (Holdings) Limited | Professional & scientific | 1997 |
| Cougar Industries Limited | Wholesale & retail | 1981 |
| Cougar Pump Repairs Limited | Manufacturing | 1984 |
| Cougar Pumps Ltd | Extraterritorial | 2003 |
| Coulson Court Freehold Limited | Extraterritorial | 2014 |
| County Hotels Group Limited | Hospitality | 1996 |
| County Hotels Limited | Hospitality | 1996 |
| Courvello Ltd | Professional & scientific | 2014 |
| Couth Limited | Professional & scientific | 2018 |
| Cowjuicemotion Limited | Professional & scientific | 2019 |
| Cragness Retail Consulting Limited | Professional & scientific | 2020 |
| Crana Holdings Ltd | Financial services | 2025 |
| Crank Power Limited | Manufacturing | 2022 |
| Create Space & Design Ltd | Arts & recreation | 2013 |
| Create Your True Balance Ltd | Education | 2020 |
| Creativalley Limited | Information & communication | 2022 |
| Creative Conjury Limited | Arts & recreation | 2024 |
| Creative Engineers Network Ltd | Information & communication | 2026 |
| Creative Insight Talking Therapies Limited | Health & social care | 2018 |
| Creative Wellbeing Community Ltd | Education | 2026 |
| Creature Music Ltd. | Manufacturing | 1990 |
| Creed Stewardship Limited | Real estate | 2023 |
| Criterion Publishing Limited | Information & communication | 1996 |
| Crmstorm Ltd | Information & communication | 2010 |
| Croft (101) Limited | Construction | 2023 |
| Croft (102) Limited | Construction | 2023 |
| Croft (103) Limited | Construction | 2023 |
| Croft (104) Limited | Construction | 2023 |
| Crossoak Pharma Limited | Information & communication | 2008 |
| Crossways Estates Limited | Real estate | 2017 |
| Crown Meadows (Berkhamsted) Management Limited | Households | 1994 |
| CS Scott Accounting LLP | | 2017 |
| Cshr Ltd | Administrative & support | 2013 |
| CSS FIM Limited | Professional & scientific | 2023 |
| CTM Property Group Ltd | Real estate | 2024 |
| CTM Tech Ltd | Information & communication | 2017 |
| Cubed 3 Developments Ltd | Construction | 2022 |
| Cubed Construction Limited | Construction | 2019 |
| Cummins Property Ltd | Real estate | 2013 |
| Cumulo Consulting Ltd | Administrative & support | 2011 |
| Cumulo UN Limited | Financial services | 2024 |
| Cure Physio Limited | Health & social care | 2019 |
| Currensea Limited | Information & communication | 2018 |
| Curx Pharma Limited | Manufacturing | 2025 |
| Cutology Hair LAB Ltd | Other services | 2022 |
| Cyber Curio LLP | | 2016 |
| Cyprus Mezze Ltd | Hospitality | 2018 |
| D & S Solutions Limited | Information & communication | 1995 |
| D C Fear Electrical Limited | Construction | 2003 |
| D Garrod Limited | Financial services | 2018 |
| D R W Designs Limited | Other services | 2015 |
| D&S Studio Ltd | Professional & scientific | 2023 |
| D.K. Heating Systems Ltd | Administrative & support | 1995 |
| Dabroch Limited | Construction | 2021 |
| DAC Surveys Ltd | Professional & scientific | 2012 |
| Daisy CUP Ltd | Wholesale & retail | 2020 |
| Daisy Recruit Ltd | Administrative & support | 2025 |
| Dalberg Property Management Ltd | Households | 2006 |
| Daljji Care Limited | Health & social care | 2020 |
| Daljji Properties Limited | Real estate | 2020 |
| Dallas Land Partners Ltd | Real estate | 2023 |
| DAN Curtis Props Limited | Information & communication | 2019 |
| DAN Moran Colour Ltd | Professional & scientific | 2019 |
| Dancing in the Dark Ltd | Education | 2026 |
| Daniel Bunting Garden Contractors Limited | Administrative & support | 2003 |
| DAR Papillon Limited | Real estate | 2003 |
| Dark FOG Films Limited | Information & communication | 2012 |
| Darkside IT Limited | Information & communication | 2013 |
| Darryl Keen Consulting Ltd | Professional & scientific | 2022 |
| Database Help Ltd | Information & communication | 2013 |
| Dave Boxall Cyber Resilience Consulting Limited | Information & communication | 2026 |
| Dave Chisnall Darts Ltd | Arts & recreation | 2019 |
| Davern Partners LLP | | 2012 |
| Daverns Audit Services Limited | Professional & scientific | 2012 |
| David C Rayner Limited | Professional & scientific | 2024 |
| David Gordon Consulting Limited | Professional & scientific | 2019 |
| David Masters Ltd | Other services | 2010 |
| David Miller Consulting Limited | Information & communication | 2010 |
| David& Ltd | Professional & scientific | 2020 |
| Dawnfray Limited | Information & communication | 2023 |
| DAX Life Sciences Ltd | Administrative & support | 2026 |
| DCM Talent Limited | Administrative & support | 2026 |
| DE Hoest Partnership Limited | Administrative & support | 2006 |
| DE Lisle Limited | Wholesale & retail | 2008 |
| Deborah Edwards Coaching Ltd | Health & social care | 2022 |
| Decadence Productions Limited | Arts & recreation | 2024 |