| Ciessey Sons and Daughters Ltd | Harlow | 2025 |
| Cifer Data Systems Limited | Frome | 1992 |
| CIG Calon Cymru 2010 CYF | Newport | 2010 |
| CIG Cerion Meats Ltd | Pwllheli | 2012 |
| CIG Cynfal CYF | Blaenau Ffestiniog | 2024 |
| CIG Engineering and Anodising Ltd | Swindon | 2025 |
| CIG Eryri - Snowdonia Meats CYF | Blaenau Ffestiniog | 2019 |
| CIG OEN Caron CYF | Tregaron | 2025 |
| CIG Print Ltd | Chester | 2024 |
| CIG Tools Ltd | Chippenham | 2025 |
| Cigairette Ltd. | Tavistock | 2021 |
| Cigar Holdings Ltd | London | 2024 |
| Cigar Tech Limited | Birmingham | 2024 |
| Cigol Controls Limited | Colyton | 1978 |
| CIH Belting Limited | Llay | 2018 |
| Ciina Limited | London | 2019 |
| Ciiore Ltd | London | 2025 |
| Cijjet Ltd | London | 2018 |
| CIL Systems Ltd | Braintree | 2022 |
| Cila's Secret Limited | Southampton | 2020 |
| Cilamure Ltd | London | 2024 |
| Cilantro FM Ltd | London | 2017 |
| Cilia FOX Limited | Glasgow | 2022 |
| Ciliang International Limited | Stafford | 2023 |
| Cilla Knitwear Ltd | Manchester | 2018 |
| Cillian & Rose Bespoke Furniture Ltd | Manchester | 2025 |
| Cilong Trade Limited | Lisburn | 2024 |
| CIM International Ltd | London | 2025 |
| CIM Services Ltd | Fareham | 2026 |
| Cimad Ltd | Dundee | 2025 |
| Cimamco Limited | Altrincham | 2012 |
| Cimatti Limited | Northampton | 2025 |
| Cimatti Renewables Ltd | Llandudno | 2026 |
| Cimbria Holdings Limited | London | 2012 |
| Cimc Trailers Co., Ltd | Beckenham | 2024 |
| Cimix Limited | London | 2025 |
| Cimla Forge Ltd | Neath | 2014 |
| Cimoro Limited | Richmond | 2014 |
| Cimosx Ltd | Mildenhall | 2025 |
| Cimpina Limited | Belfast | 1990 |
| Cimpol Limited | Huddersfield | 2014 |
| Cimsa Cement UK Limited | London | 2023 |
| Cimtech Ltd | Barry | 2022 |
| Cinaco Ltd | Southampton | 2023 |
| Cinar's Sauce Ltd | Yateley | 2019 |
| Cinch Connectivity Solutions Limited | Chelmsford | 1986 |
| Cinch Connectors Limited | Nottinghamshire | 1987 |
| Cinch Corsets Limited | Holywood | 2015 |
| Cinch Drinks Ltd | Horsham | 2024 |
| Cinch Managed Services Limited | London | 1987 |
| Cinchortho Ltd | Coleraine | 2024 |
| Cincom Mokotech UK Limited | Brentford | 2023 |
| Cindamagchem Group Co., Ltd | Manchester | 2023 |
| Cinderbake Ltd | Widnes | 2023 |
| Cinderella Golf CIC | Smethwick | 2025 |
| Cinderella Lighting Ltd | Manchester | 2020 |
| Cinderhill Spinning Company Limited(The) | Todmorden | 1959 |
| Cinders Barbecues Limited | Keighley | 1988 |
| Cindystea Limited | Galashiels | 2015 |
| Cine Masters Ltd | Royal Berkshire | 2024 |
| Cine Power International Limited | Devon | 1989 |
| Cine-Star Media Ltd | Northampton | 2022 |
| Cineaero Limited | Salisbury | 2021 |
| Cinecraft Ltd | Horley | 2024 |
| Cinejade Limited | Birkenhead | 2017 |
| Cinelux Ltd | Bristol | 2023 |
| Cinema Acoustic Treatment Systems Limited | Paisley | 2015 |
| Cinema Printing Company London Ltd | Alton | 2014 |
| Cinema Sound Ltd | Redditch | 2010 |
| Cinemack Media Ltd | Melton Mowbray | 2020 |
| Cinemascape Ltd | | 2009 |
| Ciner Glass Ltd | London | 2019 |
| Ciner Glass Productions Ltd | London | 2020 |
| Ciner Glass Property Ltd | London | 2020 |
| Cinergy Ltd | Worcester | 2025 |
| Cinescope Limited | London | 2016 |
| Cinesteel Services Limited | Borehamwood | 2025 |
| Cinetech UK Ltd | Alton | 2011 |
| Cinetex Ltd | Portsmouth | 2020 |
| Cinetic Carbon Compounds Limited | Keighley | 2003 |
| Cinetronix Ltd | London | 2023 |
| Ciniture Ltd | Weymouth | 2021 |
| Cinkivitch Ltd | Redcar | 2024 |
| Cinmech Services Limited | Glasgow | 1975 |
| Cinnaful Ltd | London | 2022 |
| Cinnamon Aitch Limited | Birmingham | 2002 |
| Cinnamon Bakery Ltd | Hull | 2022 |
| Cinnamon BUN Limited | London | 2024 |
| Cinnamon by Abdi Ltd. | Birmingham | 2025 |
| Cinnamon Framing Ltd | Thames Ditton | 2025 |
| Cinnamon Gardens Private Limited | London | 2013 |
| Cinnamon Manufacturing Ltd | Middleton | 2014 |
| Cinnamon Moon Ltd | London | 2021 |
| Cinnamon Twist Limited | Pickering | 2003 |
| Cinoci Limited | Birmingham | 2024 |
| Cinque Energy Solutions Limited | Oldham | 2003 |
| Cinque Ports GIN Ltd | Bromley | 2023 |
| Cinque Ports Rowing CIC | Faversham | 2020 |
| Cinquecento (London) Limited | Ilford | 2021 |
| Cinram Operations UK Limited | London | 1996 |