| Comptab Ltd | Professional & scientific | 2021 |
| Compuco Cloud Limited | Information & communication | 2018 |
| Compuco Services Limited | Information & communication | 2024 |
| Compucorp Holdings Limited | Financial services | 2019 |
| Compucorp Limited | Information & communication | 1977 |
| Compupoint Limited | Information & communication | 1995 |
| Computer Commerce Holdings Ltd | Professional & scientific | 2003 |
| Computer Commerce Limited | Professional & scientific | 2000 |
| Conceive Media Ltd | Information & communication | 2012 |
| Concept M&E Limited | Construction | 2010 |
| Concept Television Studios Limited | Information & communication | 2004 |
| Condra Consultancy Limited | Professional & scientific | 2009 |
| Confederation of Aerial Industries Limited | Other services | 1989 |
| Connaught Property Group Ltd | Real estate | 2025 |
| Connect Red Hearts Ltd | Health & social care | 2016 |
| CONNECT2 Community Engagement Limited | Information & communication | 2016 |
| Connemara U.K. Limited | Administrative & support | 2003 |
| Connor Construction (Watford) Limited | Construction | 2000 |
| Conrad Foods Ltd | Manufacturing | 2017 |
| Conroy Electrics Ltd | Construction | 2021 |
| Conseil Avant Ltd | Professional & scientific | 2011 |
| Consiliaris Digital Systems Ltd | Information & communication | 2021 |
| Consiliaris Healthcare Limited | Information & communication | 2026 |
| Consilio Interiors Limited | Wholesale & retail | 2017 |
| Consort Media Limited | Manufacturing | 2015 |
| Conspro Ltd | Construction | 2022 |
| Constance Priority Healthcare Limited | Health & social care | 2021 |
| Construction by Peter Ltd | Construction | 2019 |
| Construction Development Centre Ltd | Education | 2015 |
| Construction Force Recruitment Limited | Administrative & support | 2018 |
| Consult HM Limited | Professional & scientific | 2015 |
| Consultech Solutions Group Limited | Financial services | 2023 |
| Consulting RO Ltd | Professional & scientific | 2010 |
| Consumable Power Ltd | Administrative & support | 2023 |
| Contained Wellness Ltd | Arts & recreation | 2024 |
| Conte DI Savoia Limited | Wholesale & retail | 2011 |
| Contract Taxis Ltd | Transport & logistics | 2022 |
| Contractor Expert Construction Ltd | Construction | 2019 |
| Contrans Haulage Ltd | Transport & logistics | 2022 |
| Control Focus Limited | Professional & scientific | 2007 |
| Controlled Plant Enviroments Ltd | Professional & scientific | 2026 |
| Converged Building Solutions Limited | Information & communication | 2015 |
| Converged IT Ltd | Information & communication | 2019 |
| Conversational Accountancy Ltd | Extraterritorial | 2023 |
| Conversational Accountants Ltd | Extraterritorial | 2023 |
| Cool Beans Property Limited | Real estate | 2019 |
| Coolpave Limited | Administrative & support | 2016 |
| Coooly Ltd | Information & communication | 2025 |
| Cooper Court Management Company Limited | Households | 2006 |
| Cooper Square (Maidenhead) Management Company Limited | Households | 2022 |
| Copias Talent Management Ltd. | Professional & scientific | 2016 |
| Copley Duncan Surveyors Limited | Professional & scientific | 2014 |
| Coppergreen Developments Limited | Hospitality | 2007 |
| Coppertree Construction Ltd | Construction | 2025 |
| Coppice Gate Ltd | Real estate | 2022 |
| Copse Farm Management Company Limited | Households | 2007 |
| Copse Valley Homes Ltd | Real estate | 2021 |
| Corallian Heights Management Company Limited | Households | 2023 |
| Corebridge Talent Solutions Limited | Administrative & support | 2025 |
| Coretronic Investment Limited | Financial services | 2021 |
| Cork Eire Ltd | Hospitality | 2016 |
| Corn Barn Close (Beauchamp Roding) Management Company Limited | Households | 2016 |
| Cornelia Gardens Management Limited | Households | 2014 |
| Corner Farm Place Residents Company Limited | Extraterritorial | 2008 |
| Cornerstone Home Developments Ltd | Construction | 2025 |
| Cornford Roofing Ltd | Construction | 2020 |
| Cornwall Road Properties Limited | Real estate | 1994 |
| Corporate Chauffeurs Limited | Transport & logistics | 2006 |
| Corporate Mind Management Limited | Professional & scientific | 2004 |
| Corporate Refugees Limited | Administrative & support | 2015 |
| Corrigan Building Development Ltd | Construction | 2019 |
| Coryan Limited | Hospitality | 2015 |
| COS SGA Ltd | Construction | 2025 |
| Cosconst Ltd | Construction | 2025 |
| Cosmolot Limited | Professional & scientific | 2025 |
| Cosmos Food Wholesale Ltd | Wholesale & retail | 2026 |
| Costa Property Services Ltd | Hospitality | 2021 |
| Costamartina Ltd | Construction | 2018 |
| Cosyfish Limited | Arts & recreation | 2019 |
| Cottage Farm (Oadby) Residents Management Company Limited | Households | 2019 |
| Cottenham Grove Management Company Limited | Households | 2021 |
| Countisbury Gardens Management Company Limited | Households | 1982 |
| Counton Tutoring Ltd | Education | 2025 |
| Countryfile Limited | Construction | 1962 |
| Coupland Copy Ltd | Professional & scientific | 2023 |
| Coupland Solutions Ltd | Information & communication | 2014 |
| Courtney Property Services Limited | Construction | 2025 |
| Cowlyd Property Management (Prestatyn) Limited | Households | 2004 |
| Cowslip Meadow Management Company Limited | Households | 2011 |
| Coyaba Collective Ltd | Wholesale & retail | 2020 |
| Cozymedical Limited | Health & social care | 2019 |
| CP Plastering Ltd | Extraterritorial | 2023 |
| Cpoint Ltd | Construction | 2014 |
| Cqats Ltd | Education | 2013 |
| Crack Team Limited | Wholesale & retail | 2016 |
| Crafts Camera Services Ltd | Information & communication | 2022 |
| Craftsmen Door Creations Limited | Manufacturing | 2025 |
| Craig Bruce Electrical & General Ltd | Construction | 2023 |
| Craig Elve Ltd | Information & communication | 2020 |
| Cranberry Close Management Limited | Households | 2015 |