| Claire Andrews Performance Academy Limited | Arts & recreation | 2023 |
| Clancy Accountancy Limited | Professional & scientific | 2015 |
| Clapham Associates Limited | Administrative & support | 2009 |
| Clara James Tutoring Ltd | Education | 2013 |
| Claridge Customs Limited | Manufacturing | 2019 |
| Clarity Co Management Limited | Arts & recreation | 2025 |
| Clark Design Group Ltd | Professional & scientific | 2021 |
| Clark Interior Contract Services Limited | Construction | 2002 |
| Clart Limited | Other services | 2024 |
| Clarverdo Ltd | Professional & scientific | 2025 |
| Classic Assets Ltd | Information & communication | 2012 |
| Classic Candy Company Limited | Wholesale & retail | 2012 |
| Classic Quality Limited | Information & communication | 1995 |
| Classic Radio Systems Limited | Wholesale & retail | 2005 |
| Classics and Collectors Auctions Ltd | Wholesale & retail | 2024 |
| Claydon Garden Company Limited | Professional & scientific | 2007 |
| Claydon Management Consultancy Limited | Professional & scientific | 2008 |
| Clays Fire Extinguisher Services Limited | Other services | 2025 |
| Clayton's Cleaning Ltd | Administrative & support | 2024 |
| Clean Air Renewables Limited | Construction | 2021 |
| Clean Arya Ltd | Extraterritorial | 2024 |
| Clean Getaway Auto Services Ltd | Wholesale & retail | 2014 |
| Clean Loyal Solutions Group Ltd | Administrative & support | 2024 |
| Clean Loyal Solutions Limited | Administrative & support | 2024 |
| Clean Loyal Solutions Services Ltd | Administrative & support | 2024 |
| Clean My Carbon Ltd | Wholesale & retail | 2020 |
| Clean Pharmaceuticals Ltd | Wholesale & retail | 2025 |
| Clean Planet Solar Farm Limited | Construction | 2021 |
| Clean Slate Capital Limited | Financial services | 2026 |
| Clean Tech Bess Recycling - SPV1 Deeside Limited | Administrative & support | 2024 |
| Clean Tech Bess Recycling - SPV1 Hull Limited | Administrative & support | 2024 |
| Clean Tech Solar Recycling - SPV1 Hull Limited | Administrative & support | 2024 |
| Clean Tech Solar Recycling - SPV2 Deeside Limited | Administrative & support | 2024 |
| Cleanforce Limited | Administrative & support | 1993 |
| Cleaning Partners Ltd | Administrative & support | 2022 |
| Clear Choice Construction Limited | Construction | 2015 |
| Clear CUT Construction Build Ltd | Construction | 2021 |
| Clear Edge Upvc Limited | Manufacturing | 2017 |
| Clear Impressions (Research) Limited | Information & communication | 2001 |
| Clear Margins Limited | Health & social care | 2016 |
| Clear.Ears UK Limited | Health & social care | 2025 |
| Clearfields Farm Limited | Agriculture & fishing | 1982 |
| Clearframe Creative Studio Ltd | Professional & scientific | 2026 |
| Clearline Property Group Ltd | Real estate | 2026 |
| Clearpay Merchant Services Ltd | Other services | 2019 |
| Clearview Plus Ltd | Administrative & support | 2026 |
| Cleaver Construction Ltd | Construction | 2025 |
| Clever Heating & Cooling Solutions Ltd | Construction | 2018 |
| Clever Monkey Finance Ltd | Other services | 2022 |
| Clever Panda Ltd | Wholesale & retail | 2023 |
| Cleverhill Group Limited | Professional & scientific | 2019 |
| Clientsinfocus Limited | Health & social care | 2013 |
| Clieweb Limited | Information & communication | 2018 |
| Clifden Arms Events Ltd | Hospitality | 2018 |
| Clifden Arms Trading Ltd | Hospitality | 2018 |
| Climat BCT Ltd | Administrative & support | 2023 |
| Climate Solutions Specialist Ltd | Construction | 2025 |
| Climateguard Glazing Limited | Construction | 2023 |
| Clincello Ltd | Wholesale & retail | 2020 |
| Clive's Drives Limited | Construction | 2003 |
| Clobb Properties Limited | Construction | 1986 |
| Clock & Chimes Rickfords Hill (Aylesbury) Management Ltd | Real estate | 2023 |
| Close Perspectives Limited | Information & communication | 2022 |
| Cloud 9 IT Solutions Ltd | Information & communication | 2011 |
| CLOUD23 UK IT Consulting Services Ltd | Information & communication | 2022 |
| Cloudkit Ltd | Information & communication | 2022 |
| Cloudninebakes Ltd | Manufacturing | 2025 |
| Cloudscale Recruitment Ltd | Administrative & support | 2023 |
| CLR Associates Development Consulting Ltd | Professional & scientific | 2011 |
| Club 22 Clothing Limited | Wholesale & retail | 2025 |
| CM Integrations Ltd | Professional & scientific | 2026 |
| CM Scenic Services Ltd | Construction | 2025 |
| CMA Accounting Services Limited | Professional & scientific | 2023 |
| CMA Estates Limited | Real estate | 2020 |
| Cmf-International Limited | Administrative & support | 2026 |
| CMH Building Limited | Extraterritorial | 2003 |
| CMH Developments Limited | Extraterritorial | 2003 |
| CMH Services Limited | Professional & scientific | 2003 |
| CMJ Marketing Limited | Administrative & support | 2007 |
| Cmmo Property Limited | Real estate | 2023 |
| CMS Blotter Limited | Manufacturing | 2004 |
| CNF Precision Engineering Limited | Manufacturing | 1977 |
| CNM Enterprises Limited | Information & communication | 2023 |
| CNR Digital Ltd | Information & communication | 2026 |
| Coad Optical Limited | Health & social care | 2026 |
| Coastal Mini Coaches Ltd | Transport & logistics | 2010 |
| Coastgrove Limited | Real estate | 2007 |
| Coastline Trades Limited | Wholesale & retail | 2025 |
| Cobb (GB) Limited | Wholesale & retail | 2007 |
| Coburn Ward Projects Limited | Professional & scientific | 2008 |
| Cocomazzi Media Ltd | Information & communication | 2025 |
| Coconet Limited | Professional & scientific | 2016 |
| COD Kitchen Ltd | Hospitality | 2023 |
| Codemu Property Deals Ltd | Households | 2025 |
| Codii Ltd | Information & communication | 2021 |
| Codrus Fire Detection Systems Limited | Manufacturing | 1995 |
| COE Industries Ltd | Manufacturing | 2024 |
| Coffee at 108 Ltd. | Hospitality | 2017 |
| Coffee Novice Ltd | Wholesale & retail | 2020 |
| Coffee Station Aylesbury Limited | Hospitality | 2014 |