| Class One Maintenance Services Limited | Construction | 2006 |
| Classic Automobiles Worldwide Limited | Wholesale & retail | 1999 |
| Classic Car Placement Limited | Administrative & support | 2017 |
| Classic Care Limited | Health & social care | 1990 |
| Classic Food & Wine Ltd | Real estate | 2020 |
| Classic Invest Limited | Real estate | 2020 |
| Classic Nightwear Ltd | Wholesale & retail | 2011 |
| Classic Touch Wheels Ltd | Wholesale & retail | 2022 |
| Claudia Brown Body Transformations Ltd | Health & social care | 2020 |
| Claudio Pedro Paris Consultancy Limited | Professional & scientific | 2019 |
| Claudio Silvestrin Limited | Professional & scientific | 2015 |
| Claus Decor Ltd | Construction | 2018 |
| Clavering Supermarket Limited | Wholesale & retail | 2005 |
| Clavis Capital Ltd | Administrative & support | 2016 |
| Clavora Limited | Information & communication | 2026 |
| Claypots Curry Ltd | Hospitality | 2018 |
| Clboh Limited | Health & social care | 2021 |
| CLC Cars Ltd | Transport & logistics | 2025 |
| CLD Building Services Limited | Construction | 2015 |
| Clean and Polish Ltd | Administrative & support | 2021 |
| Clean and Scrub Ltd | Administrative & support | 2021 |
| Clean Clover Limited | Administrative & support | 2025 |
| Clean Clubb Ltd | Other services | 2023 |
| Clean Energy Planet Ltd | Other services | 2021 |
| Clean Energy Systems Limited | Other services | 2010 |
| Clean UPP Ltd | Administrative & support | 2021 |
| Clean Your Property Ltd | Administrative & support | 2023 |
| Clean-Ton Commercial Limited | Administrative & support | 2004 |
| Cleaning Hands Ltd | Administrative & support | 2021 |
| Cleaning Logistics (SW) Ltd | Administrative & support | 2003 |
| Cleaning Masters Direct Ltd | Administrative & support | 2021 |
| Cleanshet Ltd | Manufacturing | 2023 |
| Cleanwash (Wembley) Limited | Other services | 2019 |
| Clear Enterprises Consulting Limited | Professional & scientific | 2013 |
| Clear Enterprises Property Limited | Construction | 2016 |
| Clear Ice Cups Limited | Manufacturing | 2026 |
| Clear Mist Consulting Limited | Information & communication | 2015 |
| Clear Path Repairs Ltd | Construction | 2026 |
| Clear Sky Lease Limited | Real estate | 2018 |
| Clear Sky Therapy Limited | Health & social care | 2017 |
| Clear Solutions Complexity Assessments Limited | Professional & scientific | 2013 |
| Clear Water Care Homes Ltd | Health & social care | 2020 |
| Clearalpha Ltd | Information & communication | 2026 |
| Clearcalc Services Ltd | Professional & scientific | 2026 |
| Clearlight Tax Services UK Ltd | Professional & scientific | 2026 |
| Clearscope Services Limited | Professional & scientific | 2020 |
| Clearsight Clinic Limited | Health & social care | 2020 |
| Clearview Financial Media Limited | Information & communication | 2009 |
| Clearview IT Solutions Ltd | Information & communication | 2026 |
| Clearview Window Cleaning (Midlands) Limited | Administrative & support | 2021 |
| Clearwater Advisers Limited | Professional & scientific | 2004 |
| Cleef Ltd | Wholesale & retail | 2022 |
| Clerkenwell Design Ltd | Construction | 2018 |
| Clerkenwell House Management Company Ltd | Households | 2025 |
| Clerkenwell Screws Limited | Wholesale & retail | 1959 |
| Clever Comms Consulting Ltd | Information & communication | 2022 |
| Clever Cubs Limited | Health & social care | 2019 |
| Clever Finance Ltd | Financial services | 2025 |
| Clever Financial Services Ltd | Financial services | 2014 |
| Clever Quarters Ltd | Real estate | 2025 |
| CLG Facades Ltd | Construction | 2024 |
| Click & Alcohol 24/7 Ltd | Wholesale & retail | 2025 |
| Click & Have IT Ltd | Wholesale & retail | 2022 |
| Click Cuba Ltd | Real estate | 2019 |
| Click IT Kids Limited | Administrative & support | 2000 |
| Click Services London Ltd | Construction | 2021 |
| CLICK2DEPLOY Ltd | Information & communication | 2022 |
| CLICK2REACH Ltd | Information & communication | 2013 |
| Clickback Limited | Professional & scientific | 2003 |
| Clickgo Market Ltd | Wholesale & retail | 2022 |
| Clicknbook Limited | Administrative & support | 2025 |
| Clieveden (Poole) Limited | Households | 2004 |
| Clifford and Lockley Limited | Construction | 2023 |
| Clifford Project Services Limited | Professional & scientific | 2018 |
| Cliffords Dynamic Ltd | Administrative & support | 2008 |
| Clifftop Consulting Limited | Professional & scientific | 2025 |
| Clift Ltd | Wholesale & retail | 2025 |
| Climaco & Bautista Company Limited | Health & social care | 2019 |
| Climate Proof Ltd | Information & communication | 2023 |
| Climax London Limited | Real estate | 2020 |
| Climb UP Limited | Real estate | 2002 |
| Clinglobal Limited | Wholesale & retail | 2014 |
| Clinic & Health Management Ltd | Health & social care | 2022 |
| Clinic Flow Marketing Ltd | Professional & scientific | 2026 |
| Clinical Build Limited | Manufacturing | 2024 |
| Clinical Connexx Limited | Professional & scientific | 2013 |
| Clinical Optical Limited | Health & social care | 2002 |
| Clinical Trials Innovations Limited | Professional & scientific | 2015 |
| Clinidirect Pharma UK Ltd | Administrative & support | 2020 |
| Clinikal Ltd | Professional & scientific | 2013 |
| Clinonc Consultations Ltd | Health & social care | 2022 |
| Clip Claims 2015 Limited | Professional & scientific | 2015 |
| Clive A.Burden Limited | Wholesale & retail | 1971 |
| Clive Christian London Limited | Construction | 2009 |
| Clive Desilva Limited | Administrative & support | 2015 |
| Clive Lawrence & Co Limited | Real estate | 2000 |
| Cliveden Court Management Company Limited | Households | 2009 |
| Cllu Ltd | Transport & logistics | 2025 |
| Cloadtest Ltd | Information & communication | 2013 |
| Clock Tower Management Limited | Real estate | 2010 |