| Cinque Ports Sweep Limited | Winchelsea | 2014 |
| Cinqueport Limited | Kingsbridge | 2015 |
| Cinven Foundation | London | 2007 |
| Cinzia Campigotto Limited | London | 2004 |
| CIO Connect Limited | Warwick | 2007 |
| Ciobanu Holdings Ltd. | Ipswich | 2025 |
| CIP Bathroom Fitter Limited | Taunton | 2021 |
| Cippenham Shared Church Trust Limited | Cippenham | 1969 |
| Cipri Barber Limited | Oldham | 2024 |
| Cipri Services Ltd | Southend-On Sea | 2019 |
| Ciprian Diaconu Ltd | Northampton | 2017 |
| Ciprian Tudose Ltd | Bath | 2022 |
| Cips Africa Ltd | Peterborough | 2015 |
| CIQ Enterprises Limited | Ross-On-Wye | 2025 |
| Cir-Comm Systems Limited | Nottingham | 1989 |
| Circadia Group Limited | London | 2025 |
| Circadian BTS Limited | Bristol | 2025 |
| Circe Beauty Studio Limited | Twickenham | 2024 |
| Circe Holdings Ltd | Gateshead | 2025 |
| Circe Piercings Limited | Derby | 2022 |
| Circelli N & Co Limited | Ipswich | 2017 |
| Circinn (Scotland) Limited | Dundee | 2014 |
| Circle 2 Success Limited | Cheltenham | 2013 |
| Circle Arch Ltd | Manchester | 2024 |
| Circle Automotive Ltd | Epping | 2014 |
| Circle Barbers Ltd | Carshalton | 2021 |
| Circle Drive Ltd | Colchester | 2024 |
| Circle Foundation Limited | London | 2025 |
| Circle Funerals Ltd | Altrincham | 2021 |
| Circle Health Myway Limited | London | 2022 |
| Circle London Management Limited | Hertford | 2021 |
| Circle Massage Therapy Limited | Henley-On-Thames | 2017 |
| Circle Mediation Limited | Reading | 2023 |
| Circle of Influence Ltd | London | 2022 |
| Circle of Safety Training Services Limited | Banchory | 2018 |
| Circle of Vigour Ltd | Milton Keynes | 2024 |
| Circle of Young Intrapreneurs Ltd | London | 2016 |
| Circle One Concierge Limited | Wilmslow | 2025 |
| Circle Plus Security Ltd | Hatfield | 2020 |
| Circle Search Limited | Cardiff | 2019 |
| Circle Square 24 Ltd | Newport | 2020 |
| CIRCLE08 Limited | Stanmore | 2018 |
| CIRCLE08 Media Limited | Stanmore | 2021 |
| CIRCLE84 Limited | London | 2014 |
| Circleline Design Studio Limited | Edgware | 2012 |
| Circleone Technologies Limited | Leicester | 2020 |
| Circles and Squares Limited | London | 2014 |
| Circles South East | Didcot | 2008 |
| Circleup Ltd | Lingfield | 2024 |
| Circolar Ltd | London | 2022 |
| Circu Limited | Fareham | 2000 |
| Circuit Automotive Limited | Uxbridge | 2024 |
| Circuit Break Retreats Limited | Bristol | 2023 |
| Circuit Breaker Specialists Limited | Amlwch | 2019 |
| Circuit Graphics Limited | Chelmsford | 1995 |
| Circuitswop Ltd | Manchester | 2026 |
| Circular Bioeconomy Alliance Advisors Limited | London | 2023 |
| Circular Communities Scotland Ltd | Stirling | 2004 |
| Circular DO Tank Limited | London | 2024 |
| Circular Economy Industry Training & Qualifications Limited | Northampton | 2024 |
| Circular Economy Institute Limited | Northampton | 2023 |
| Circular Enterprises Limited | Stirling | 2022 |
| Circular Margate CIC | Margate | 2025 |
| Circular Mindset Guru Ltd | London | 2024 |
| Circulate Roastery Limited | Leeds | 2021 |
| Circulo Group Ltd | Rochdale | 2021 |
| Circumference FS (UK) Limited | London | 2018 |
| Circus 25 Ltd | London | 2019 |
| Circusinkuk Ltd | St. Austell | 2025 |
| Cire Limited | Lancing | 2003 |
| Cirencester Barber Shop Ltd | Cirencester | 2022 |
| Cirencester Cobbler Limited | Cirencester | 2024 |
| Cirencester Masonic Hall Limited | Glos | 1968 |
| Cirencester Nails Limited | Enfield | 2026 |
| Cirencester Physiotherapy Centre Ltd | Ingatestone | 2020 |
| Cirk HES Ltd | Helston | 2003 |
| Ciro's Barbershop Limited | London | 2025 |
| Cirowand Limited | Hampton | 1979 |
| Cirq Hiit Limited | Woodford Green | 2022 |
| Cirra Ltd | Tenby | 2026 |
| Cirrus Information Technology Limited | Bromsgrove | 2002 |
| Cirrus Purchasing Ltd | Wirral | 2007 |
| CIRRUS8 UK Limited | London | 2024 |
| Cirta Plumbling Ltd | London | 2014 |
| CIS Claims Limited | Liverpool | 2021 |
| Cisan Limited | Preston | 2019 |
| Ciscos Karma Ltd | Brighton | 2026 |
| Ciseaux Ltd | Cardiff | 2025 |
| Cismaru Barber Ltd | Canterbury | 2026 |
| Ciso Ltd | Wolverhampton | 2012 |
| Cisoselect Limited | Malton | 2019 |
| Cissbury Barns Limited | Worthing | 2025 |
| Cissbury Building Co Ltd | Worthing | 2017 |
| Cissbury Enterprises Ltd | Brighton | 2000 |
| Cissbury Property Maintenance Ltd | Hove | 2006 |
| Cissy Villa Limited | London | 2025 |
| Cisza Space Limited | Hook | 2025 |
| Citadel Insights Ltd. | London | 2019 |
| Citadel International Security Services Ltd | Chippenham | 2009 |
| Citadel Management (Europe) II Limited | London | 2020 |