| Church Farm Cafe Ltd | Hospitality | 2023 |
| CIH Electrical Limited | Construction | 2016 |
| Cimbroni Limited | Wholesale & retail | 2024 |
| Circle Therapy Ltd | Health & social care | 2019 |
| City Electrical Services Ltd | Construction | 2016 |
| City Road Markings Ltd | Construction | 2020 |
| CJ Fire & Security Ltd | Administrative & support | 2008 |
| CJ Technical Services Ltd | Construction | 2020 |
| CJS Consult Ltd | Professional & scientific | 2021 |
| CK IT Services Limited | Information & communication | 2013 |
| CKM Building & Landscaping Services Ltd | Construction | 2023 |
| Claire Garner Interiors Ltd | Wholesale & retail | 2017 |
| Clare Solomon Creative Ltd | Information & communication | 2025 |
| Clarence Barbers Limited | Other services | 2025 |
| Clayhill Consulting Ltd | Administrative & support | 2014 |
| Clientology Consulting Ltd | Professional & scientific | 2025 |
| Clips of Tring Limited | Other services | 2024 |
| Clissold Contracting Ltd | Construction | 2024 |
| Cloudarity Ltd | Information & communication | 2019 |
| Clove Street Consulting Ltd | Professional & scientific | 2026 |
| CLP Legal Consulting Limited | Professional & scientific | 2021 |
| CM Supplies (Europe) Ltd | Wholesale & retail | 2003 |
| CMC Golf Europe Ltd | Wholesale & retail | 2004 |
| CNC Wood Workshop Limited | Wholesale & retail | 2026 |
| Coaching YOU Ltd | Professional & scientific | 2019 |
| Coachment Ltd | Professional & scientific | 2024 |
| CODE17 Ltd. | Information & communication | 2016 |
| Cofix UK Ltd | Wholesale & retail | 2018 |
| Cogent ICT Limited | Information & communication | 2010 |
| Cogitatus Limited | Information & communication | 2019 |
| Cognate Ltd | Information & communication | 2020 |
| Cognitum Ltd | Information & communication | 2025 |
| Coldstream Farm Management Company Limited | Households | 2023 |
| Computely Limited | Information & communication | 2020 |
| Conduit Partners Limited | Information & communication | 2025 |
| Conex Exhibitions Ltd | Administrative & support | 2020 |
| Confio Ltd | Professional & scientific | 2020 |
| Connect Technical Services Ltd | Construction | 2017 |
| Constellation IC1805 Ltd | Professional & scientific | 2022 |
| Construction and Support Services Ltd | Construction | 2014 |
| Consult RJC Limited | Professional & scientific | 2013 |
| Content Republic Ltd | Professional & scientific | 2019 |
| Content With Purpose Limited | Information & communication | 2016 |
| Controltechpro Engineering Ltd | Professional & scientific | 2024 |
| Convert Consulting Ltd | Information & communication | 2023 |
| Convert Properties Ltd | Real estate | 2023 |
| Copley Technical Solutions Limited | Information & communication | 2019 |
| Copper Sphere Limited | Professional & scientific | 2006 |
| Corporate Agenda Limited | Professional & scientific | 2008 |
| Corporate Wellbeing Coaching Limited | Professional & scientific | 2026 |
| Corvus Developments Limited | Real estate | 2010 |
| Costea Homes Ltd | Construction | 2026 |
| Coterie Design Ltd | Professional & scientific | 2025 |
| Couch to Carbon Zero Ltd | Professional & scientific | 2022 |
| Couriers R US Limited | Transport & logistics | 2025 |
| Cowlam Studios Ltd | Professional & scientific | 2017 |
| CPD Freelance Limited | Professional & scientific | 2024 |
| CR Cars and Commercials Limited | Wholesale & retail | 2024 |
| Craft & Fiction Ltd | Information & communication | 2023 |
| Craignish Limited | Transport & logistics | 2007 |
| Crampsie Couriers Limited | Transport & logistics | 2019 |
| Craven Contracts Limited | Wholesale & retail | 2000 |
| Crawley Crossing Management Limited | Households | 2009 |
| Creative Headstart Leadership Consultancy Ltd | Professional & scientific | 2024 |
| Croci Fabrications Ltd | Construction | 2016 |
| Cross Oak (Berkhamsted) Developments Limited | Construction | 1968 |
| CS & ND Holdings Limited | Manufacturing | 2023 |
| CS Consulting Ltd | Information & communication | 2026 |
| Csaks Capital Ltd | Financial services | 2024 |
| CT Tring Ltd | Hospitality | 2023 |
| Ctop Window MAN Ltd | Construction | 2019 |
| Culverwood Electrical Ltd | Construction | 2021 |
| Cunningham Scaffolding Ltd | Construction | 2022 |
| Currie Consulting Limited | Information & communication | 2018 |
| Curtain Call Software Ltd | Professional & scientific | 2026 |
| Cutis Vitae Limited | Other services | 2025 |
| CWP Metal Work Solutions Ltd | Manufacturing | 2016 |
| D Hunter Fabrications Ltd | Manufacturing | 2023 |
| D R Chauffeurs Limited | Transport & logistics | 2020 |
| D Wilson Decorating Services Limited | Construction | 2021 |
| DAE HA Europe Ltd | Manufacturing | 2020 |
| Daffodil Communications Limited | Information & communication | 2012 |
| Dagda Automation Ltd | Information & communication | 2019 |
| Daljji Couriers Ltd | Transport & logistics | 2025 |
| Daly&Gill Ltd | Real estate | 2024 |
| DAN Robinson Design Ltd | Information & communication | 2014 |
| Daniel Shaer Shepherd Ltd | Extraterritorial | 2022 |
| Dark Crown Property Services Ltd | Construction | 2023 |
| Dash Enterprises Limited | Wholesale & retail | 2001 |
| Data MEI Limited | Information & communication | 2025 |
| Data Thinking Ltd | Information & communication | 2018 |
| Data to Value Ltd. | Information & communication | 2013 |
| Datonomics Ltd | Information & communication | 2026 |
| Dave D'Arcy Limited | Professional & scientific | 2023 |
| David Burnett Quantity Surveying Services Limited | Professional & scientific | 2013 |
| David Llewellyn Limited | Information & communication | 2024 |
| David Traherne Developments Limited | Construction | 1967 |
| Davis Electrical Ltd. | Construction | 2014 |
| Daxtrans Limited | Transport & logistics | 2017 |
| DB Consulting Herts Limited | Administrative & support | 2017 |