| Classic Valeting Limited | Extraterritorial | 2009 |
| Classics at the Farm Limited | Wholesale & retail | 2023 |
| CLE France Ltd | Administrative & support | 2009 |
| Cleamax Limited | Professional & scientific | 1974 |
| Clean Holdings Limited | Financial services | 2015 |
| Clean Supply Limited | Wholesale & retail | 2009 |
| Cleandustrial Services Limited | Administrative & support | 2011 |
| Cleaning and Property Maintenance Services Ltd | Administrative & support | 2024 |
| Cleaning Assurance Ltd | Extraterritorial | 2011 |
| Clear Water Corporation Limited | Professional & scientific | 2007 |
| Clearcall 2000 Ltd | Information & communication | 1999 |
| Clearway Consulting Ltd | Information & communication | 2008 |
| Clerkenwell Central Management Company Limited | Households | 1998 |
| Cleva Commercial Property Ltd | Real estate | 2021 |
| Clevagroup Ltd | Information & communication | 2006 |
| Clever Advice Mortgages Limited | Financial services | 2018 |
| Clever Financial Solutions Limited | Financial services | 2017 |
| Click Fusion Cloud Limited | Information & communication | 2024 |
| CLM & HLM Properties Limited | Real estate | 2026 |
| Clockwork Creative Consultancy Limited | Professional & scientific | 2019 |
| CLOUD9 Telephony Ltd | Information & communication | 2013 |
| Clovelly Holdings Ltd | Real estate | 2021 |
| Cloverleaf Foods Limited | Wholesale & retail | 1994 |
| Clslw Property Ltd | Real estate | 2023 |
| Clubking Limited | Wholesale & retail | 2003 |
| CLUTTER2CLEAR Ltd | Water & waste | 2018 |
| CM9 Consultancy Limited | Wholesale & retail | 2025 |
| Cmdred Ltd | Information & communication | 2025 |
| CMF Promotions Limited | Manufacturing | 2009 |
| CMH Grays Inn Ltd | Households | 2012 |
| CNC Property Group Ltd | Real estate | 2018 |
| CNM Project Ltd | Construction | 2023 |
| Co Protect Limited | Financial services | 2017 |
| Co-Co-B Design Limited | Wholesale & retail | 2006 |
| Co-Incidence Ventures Holdings Limited | Financial services | 2024 |
| Co-Incidence Ventures Limited | Professional & scientific | 2000 |
| COB UK Limited | Wholesale & retail | 1999 |
| Cobra Systems UK Limited | Information & communication | 2007 |
| Cocomotion | Professional & scientific | 2010 |
| Code BI Ltd | Professional & scientific | 2011 |
| Code Examples Ltd | Information & communication | 2017 |
| Coeskip Ltd | Administrative & support | 2025 |
| Cognitant Group Limited | Information & communication | 2018 |
| Cohen & Jenner Family Partnership LLP | | 2020 |
| Cojo Interiorrss Limited | Manufacturing | 2019 |
| Coker Supplies Ltd | Wholesale & retail | 2021 |
| Colborne Close (Iver) Management Company Limited | Households | 2016 |
| Colchester (Burma) Residents Company Limited | Households | 2003 |
| Coldhams Lane Cambridge Management Limited | Real estate | 2016 |
| Colesgrove Developments Limited | Construction | 2005 |
| Colin Rice Architect Ltd | Professional & scientific | 2016 |
| Colin White Developments Limited | Construction | 1991 |
| College of the Motor Industry Limited(The) | Education | 1986 |
| Colne 4 Limited | Financial services | 2003 |
| Colourspec Limited | Administrative & support | 2001 |
| Colvin Property Group Limited | Real estate | 2022 |
| Colwell Consulting Ltd | Professional & scientific | 2025 |
| Commercial Consulting Ltd | Professional & scientific | 2023 |
| Commsquest Consulting Ltd | Professional & scientific | 2010 |
| Community Development Action Hertfordshire | Health & social care | 1999 |
| Compak Systems Limited | Professional & scientific | 2001 |
| Complete Media & Marketing Limited | Administrative & support | 2000 |
| Comptons Food Service Limited | Hospitality | 2019 |
| Concord Trophies and Sportswear Limited | Wholesale & retail | 2018 |
| Connaught House (Ashford) Management Company Limited | Administrative & support | 2005 |
| Connolly Place Management Company Limited | Households | 2000 |
| Conqueror Industries Limited | Manufacturing | 1991 |
| Conrath Durrant Ltd | Construction | 2016 |
| Consider IT Catered Limited | Hospitality | 2024 |
| Consilium Consulting International Ltd | Professional & scientific | 2016 |
| Consolidated Surveying Ltd | Professional & scientific | 2011 |
| Contack Limited | Administrative & support | 2018 |
| Contract Cleaning Group Ltd | Administrative & support | 2024 |
| Contract Recruitment Group Ltd | Administrative & support | 2026 |
| Convert Water Limited | Water & waste | 2015 |
| Coogan Refractory Services Limited | Manufacturing | 2012 |
| Cook & Partners Limited | Professional & scientific | 2005 |
| Cool Canasta Limited | Information & communication | 2017 |
| Cool Network Group Limited | Wholesale & retail | 2009 |
| Coopers Mews Management Company Limited | Households | 2000 |
| Copper Thread Ltd | Professional & scientific | 2026 |
| Copy Management Services Ltd | Construction | 2007 |
| Corevision Capital Limited | Financial services | 2025 |
| Corfe Music Entertainment Limited | Information & communication | 2024 |
| Cornerman Limited | Professional & scientific | 2011 |
| Corporate & Marine Finance Limited | Financial services | 2006 |
| CORR2 Limited | Construction | 2012 |
| Cost Ltd | Wholesale & retail | 2019 |
| Costessey Developments Ltd | Real estate | 2020 |
| Cotton Place Management Company Limited | Households | 2007 |
| Coulter IT Services Limited | Information & communication | 2013 |
| Countdown Demolition Limited | Wholesale & retail | 2009 |
| Counting House Services Limited | Extraterritorial | 1996 |
| Country Garden Care Landscaping Limited | Other services | 2018 |
| County Fires Limited | Wholesale & retail | 2004 |
| County Lettings (Hertford) Ltd. | Real estate | 2001 |
| Courtlands Adeyfield Management Company Limited | Households | 1994 |
| Couvre-Feu Fire Consulting Limited | Professional & scientific | 2010 |
| COX Hair, Holistics and Beauty Therapies Ltd | Other services | 2019 |
| Cozens Farm Management Co Limited | Households | 2024 |