| Cipheredge Investment Solutions Ltd | Manchester | 2025 |
| Ciphernest Capital Ltd | Manchester | 2025 |
| Cipherquest Investment Services Ltd | Manchester | 2025 |
| Ciprocess Ltd | Bishop'S Stortford | 2004 |
| Cipure Ltd | London | 2025 |
| Ciqo Limited | Milton Keynes | 2011 |
| Circa 84 Ltd | London | 2019 |
| Circa Business Systems Limited | London | 1986 |
| Circa VOS Limited | Glasgow | 2013 |
| Circadian (CH) Limited | Battersea | 2000 |
| Circcurer Limited | Harrogate | 2023 |
| Circle Business Solutions Limited | London | 2010 |
| Circle Insurance Services (Nottingham) Ltd | Warwickshire | 2000 |
| Circle Liverpool Limited | Bolton | 2000 |
| Circle Offshore Limited | Aberdeen | 1999 |
| Circle Recruitment Ltd | Stoke On Trent | 2018 |
| Circle-Assets Ltd | St. Neots | 2023 |
| Circonix Limited | Cheltenham | 1979 |
| Circuit Centre Brooklands Limited | Weybridge | 1994 |
| Circuit Solutions Limited | Cambridge | 2007 |
| Circuitcam Ltd | Bury St. Edmunds | 2025 |
| Circuitcraft Ventures Ltd | London | 2026 |
| CIRCUL8TECH Limited | Sandbach | 2026 |
| Circular Computing Limited | Portsmouth | 2019 |
| Circular Growth Capital Limited | London | 2024 |
| Circularball Limited | Reading | 2024 |
| Circulus Limited | Chichester | 2025 |
| Circumix Ltd | London | 2023 |
| Circus Plume Limited | St Albans | 2009 |
| Circus Sauce Limited | Stroud | 2022 |
| Circus Signs Limited | Bridgwater | 2022 |
| Circusbb Ltd | Bristol | 2020 |
| Circuslondon Limited | London | 2007 |
| Cirdan Limited | Lisburn | 2016 |
| Cire Trading Co., Limited | London | 2024 |
| Cirencester Computers Limited | Cirencester | 2005 |
| Cirencester Skips Limited | Gloucestershire | 2003 |
| Cirencester Tuition Centre Ltd | London | 2021 |
| Cirent Group Co., Ltd | Beckenham | 2023 |
| Cirion Sailing Ltd. | Kington | 2025 |
| Ciro (London) Limited | Aylesbury | 1994 |
| Ciro's Pizza Pomodoro Limited | London | 1994 |
| Cirqle Bar & Cafe Limited | Doncaster | 2026 |
| Cirqle Cafe & Bar Limited | Doncaster | 2026 |
| Cirqle Cafe Limited | Doncaster | 2026 |
| Cirque London Ltd | Chorleywood | 2016 |
| Cirram Limited | Carmarthen | 2002 |
| Cirrus Cloud Ltd | Slough | 2011 |
| Cirumintercontinental Group Co., Limited | Kington | 2022 |
| CIS Club Ltd | Harrow | 2009 |
| CIS NV Limited | London | 2012 |
| CIS Polystyrene & Foam Limited | Crewe | 2022 |
| CIS Properties Limited | Bristol | 1983 |
| CIS Self Employed Limited | Chelmsford | 2013 |
| Cis-Systems (Midlands) Limited | Bedworth | 2018 |
| Cisac Limited | London | 2010 |
| Cit-E Group UK Ltd | Birmingham | 2015 |
| Citadel Associates Limited | London | 2024 |
| Citadel Leadership Limited | London | 2026 |
| Citation Fire & Electrical Limited | Wilmslow | 2002 |
| Citation Verification Limited | Manchester | 2026 |
| Citehow Limited | Haddenham | 1971 |
| Citi Afrique Company Ltd | Leicester | 2024 |
| Citi Trading Limited | Harrow | 2012 |
| Citibox Kensington Limited | London | 1986 |
| Citielectrical Limited | Nottingham | 2011 |
| Citihaulage Ltd | Rainham | 2015 |
| Citimetric Limited | Hull | 2013 |
| Citiplace Limited | Sutton | 2001 |
| Citipost Direct Distribution Limited | Erith | 2004 |
| Citipost Mail Limited | Erith | 1999 |
| Citipost Trading Limited | Belvedere | 1999 |
| Citisc Consultancy Ltd | London | 2010 |
| Citisen Ltd | London | 2022 |
| Citisolar Limited | Nottingham | 2011 |
| Citisuites Limited | Croydon | 2011 |
| Citizen Media Ltd | London | 2009 |
| Citizens Advice Scotland (Trading) Limited | Edinburgh | 2013 |
| Citizensound Limited | Croydon | 2007 |
| Citnow Ltd | Wokingham | 2016 |
| Citria Yachting Ltd | London | 2026 |
| Citrus Digital Limited | Bristol | 2009 |
| Citrus Ltd | Leicester | 2016 |
| Citta Investments Limited | London | 2008 |
| City Relocations Limited | Leigh On Sea | 2011 |
| City & County Signs Limited | Abingdon | 2015 |
| City & Suburban Industrial Limited | London | 2022 |
| City & Suburban Parking Limited | Watford | 2011 |
| City & Trust Trustees Limited | London | 1988 |
| City (R & D) Limited | Maldon | 2001 |
| City Airport Car Services Ltd | Ilford | 2014 |
| City and Suburban Ltd | London | 2016 |
| City and Walbrook (Nominees) Limited | Kenilworth | 1984 |
| City Asphalt Limited | Lenton Nottingham | 1983 |
| City Bearings & Transmission Limited | Nottingham | 2024 |
| City Bespoke Joinery Ltd | Dagenham | 2025 |
| City Bilvard Limited | London | 2022 |
| City Broadband Limited | Swindon | 2001 |
| City Capital Finance Limited | Guildford | 1998 |
| City Centre Concrete Limited | Liverpool | 2016 |