| Cinsano Wind Ltd | Beverley | 2025 |
| Cintec International Limited | Newport | 1985 |
| Cintonē Ltd | London | 2022 |
| Cinvest Ltd | London | 2025 |
| CIO Inspection Ltd | London | 2021 |
| Ciock International Co., Limited | Beckenham | 2024 |
| Cione Postural Pain (Harley ST) Ltd | Loughborough | 2000 |
| Cipark Limited | Dorridge | 1964 |
| Ciperd Ltd | Midlands | 2020 |
| Cipher Atlas Productions Ltd | Manchester | 2024 |
| Cipher Graphics Limited | Stoke On Trent | 1997 |
| Cipher Group Limited | Sheffield | 2016 |
| Cipher Surgical Limited | Edinburgh | 2010 |
| Ciprian & Corina Ltd | London | 2026 |
| Ciprian 85 Ltd | Royston | 2025 |
| Cirac Engineering Limited | Southampton | 1983 |
| Circ Manufacturing Limited | Frome | 2019 |
| Circ Realisations Limited | Ferryboat Lane | 2001 |
| Circa Coffee Holdings Ltd | Leeds, | 2026 |
| Circa Solutions CIC | Hartlepool | 2026 |
| Circablanca Limited | Shefford | 2024 |
| Circad Design Limited | Essex | 2001 |
| Circada Limited | Liverpool | 2017 |
| Circadian Lighting Limited | Stanley | 2020 |
| Circadian Solar Limited | London | 2003 |
| Circadiux Ltd | London | 2023 |
| Circatron Ltd | Tonbridge | 1983 |
| Circe London Ltd | Bury St. Edmunds | 2022 |
| Circe-Mehra Limited | Northampton | 2022 |
| Circebio UK Limited | London | 2026 |
| Circle Capital International Trading (UK) Limited | London | 2024 |
| Circle Line Limited | Harlow | 2003 |
| Circle of Pearls Ltd | London | 2025 |
| Circle One Audio Visual Limited | Cardiff | 2019 |
| Circle One Golf Ltd | Wigan | 2026 |
| Circle Pack Ltd | London | 2020 |
| Circle Performance Ltd | Abingdon | 2025 |
| Circle Plastics Limited | London | 1971 |
| Circle. Recordings Ltd. | Westbury | 2019 |
| Circled Blue Ltd | Cardiff | 2025 |
| Circletech Limited | London | 2019 |
| Circmar International Limited | London | 2021 |
| Circo Interiors Ltd | Manchester | 2018 |
| Circolo Sports Ltd | Morpeth | 2024 |
| Circomatt Ltd | Wakefield | 2024 |
| Circtec Engineering Ltd. | London | 2016 |
| Circtec Knowledge Ltd. | London | 2016 |
| Circtec Operations Ltd | London | 2021 |
| Circucel Liquid Dispensing System Limited | Armagh | 2026 |
| Circuit Breaker Sales & Maintenance Services Ltd | Pontefract | 2022 |
| Circuit CNC Limited | Chipping Campden | 2003 |
| Circuit Component Distribution Ltd | Barrow | 2007 |
| Circuit Component Supplies Ltd | Bolton | 2003 |
| Circuit Electronic Services Limited | Bridgend | 2016 |
| Circuit Engineering Marketing Company Limited | Petersfield | 1980 |
| Circuit Hydraulics Limited | Liverpool | 1984 |
| Circuit Solutions (Cambridge) Limited | Huntingdon | 1999 |
| Circuitbyte Ltd | Salisbury | 2014 |
| Circuitmaster Designs Limited | Rochdale | 1993 |
| Circuits Integrated U.K. Ltd | Guildford | 2025 |
| Circuits Manufacturing Services Limited | Hindhead | 2022 |
| Circuitz Ltd | Newport | 2024 |
| Circulabs Ltd | Todmorden | 2015 |
| Circular Aviation Ltd | London | 2024 |
| Circular Box Solutions Ltd | Swindon | 2025 |
| Circular Branding Group Ltd | Shipley | 2021 |
| Circular Carpentry & Build Co. Ltd | Reading | 2026 |
| Circular Cooling Limited | Renfrew | 2017 |
| Circular Data Solutions Limited | Belfast | 2015 |
| Circular Drinks Limited | Lampeter | 2024 |
| Circular Economy Products Limited | Blackburn | 2020 |
| Circular EV Ltd | London | 2024 |
| Circular Feedstock Services Limited | Slough | 2019 |
| Circular Group Ltd | Magherafelt | 2020 |
| Circular Healthcare Solutions Ltd | Edinburgh | 2022 |
| Circular Inc. Ltd | Brighton | 2020 |
| Circular Inks Ltd | Grimsby | 2020 |
| Circular Lighting CIC | Glasgow | 2025 |
| Circular Refining and Products Company Ltd | Manchester | 2022 |
| Circular Renewables Ltd | Goole | 2021 |
| Circular Solution Labs Limited | Peterborough | 2026 |
| Circular Squared Drinks Ltd | Lincoln | 2022 |
| Circular Sustainability Ltd | Maidenhead | 2025 |
| Circular Trail Ltd | London | 2024 |
| CIRCULAR11 Communities C.I.C. | Christchurch | 2021 |
| CIRCULAR11 Ltd | Christchurch | 2021 |
| Circularising (Southern) Limited | Sutton | 2021 |
| Circularity Furniture Ltd | Leeds | 2024 |
| Circulating Pumps Limited | Burton-On-Trent | 2001 |
| Circus Health Limited | Bath | 2019 |
| Cirdan Imaging Limited | Lisburn | 2010 |
| Cirencester Brewery Ltd | Cirencester | 2011 |
| Cirencester Fabrication Services Limited | Cirencester | 2009 |
| Cirencester Wood Finishing Limited | Cirencester | 2017 |
| Cirevon Scotland Ltd | Edinburgh | 2026 |
| Cirgraphics Limited | Rushden | 1982 |
| Cirkis Dancewear Limited | Clydebank | 2018 |
| Cirqit Limited | Uttoxeter | 2025 |
| Cirql Works Ltd | Manchester | 2025 |
| Cirrus (GB) Limited | Preston | 2002 |