| Castlegate 263 Limited | Mansfield | 2003 |
| Castlekemp Ltd | Farnham | 2011 |
| Castlepark Consulting Limited | Glasgow | 2007 |
| Castlerock & Allen Ltd | Lisburn | 2020 |
| Castleroe Pre-Cast Concrete Limited | Co Londonderry | 2002 |
| Castles Buildings Limited | Barnsley | 2003 |
| Castles Technology UK & Ireland Ltd | Salisbury | 2020 |
| Castles UK (Mattresses) Limited | York | 2007 |
| Castlespeed Ltd | Coalville | 2023 |
| Castlesprings Limited | Manchester | 2012 |
| Castlet Limited | Lincolnshire | 1999 |
| Castleton Textiles Limited | Bacup | 1992 |
| Castleton Tyres Ltd | Rochdale | 2025 |
| Castlewood Joinery Limited | Ashbourne | 2002 |
| Castlewood Kitchens (NI) Ltd | Magherafelt | 2013 |
| Castlewood Projects Ltd | Doncaster | 2023 |
| Castlewood Vineyards Ltd | Axminster | 2016 |
| Castorblanc Ltd | London | 2025 |
| Castors and Wheels Direct Limited | Birmingham | 1998 |
| Castree Projects Limited | Chester | 2013 |
| Castrovillari Ltd | London | 2018 |
| Castrusions Ltd. | Wolverhampton | 2024 |
| Caststitch Engineering Limited | Congleton | 1982 |
| Caststone Direct Limited | Rochford | 2018 |
| Caststonesupplier UK Ltd | Hull | 2023 |
| Casu Consulto Limited | Penryn | 2003 |
| Casual PUB & Restaurants Ltd | Sawbridgeworth | 2024 |
| Casual Tees Limited | Fyfield | 2003 |
| Casually Dazzling Ltd | London | 2019 |
| Casuals Corner Ltd | London | 2022 |
| Caswell & Company Limited | Corby | 1920 |
| Caswell Carpentry Limited | Redruth | 2025 |
| Caswick Limited | Doncaster | 1985 |
| Caswood Limited | Wakefield | 1995 |
| Cat Burglar Dough Co Ltd | Littlehampton | 2021 |
| Cat DRY Ltd | Cardiff | 2025 |
| Cat Goalkeeping Products Ltd | Maidstone | 2022 |
| Cat International Ltd | Hixon | 2007 |
| Cat Pumps (U.K.) Limited | Weybridge | 1975 |
| Cat Purrch Ltd | Saint Leonards-On-Sea | 2026 |
| Cat Saws Ltd | Wellingborough | 2021 |
| Cat's Whisker Technologies Limited | Ashtead | 2009 |
| Cat-Aviation Limited | Hitchin | 2014 |
| Catabolic Chemicals Ltd | Leeds | 2021 |
| Catalco (NO.1) Ltd | Widnes | 2019 |
| Cataleia Automotive Ltd | Haverfordwest | 2025 |
| Catalent CTS (Edinburgh) Limited | Swindon | 2004 |
| Catalent Micron Technologies Limited | Swindon | 1980 |
| Catalent MTI Pharma Solutions Limited | Swindon | 2012 |
| Catalent Oxford Limited | London | 2022 |
| Catalent U.K. Swindon Zydis Limited | Glasgow | 1980 |
| Catalent UK Supply Chain Limited | Nottingham | 1989 |
| Catalin Andrei Ltd | Birmingham | 2018 |
| Catalin Auto Repair Limited | Mansfield | 2023 |
| Catalin BZR Ltd | London | 2025 |
| Catalina (UK) Limited | Hampshire | 2002 |
| Catalina Beauty Group Limited | Beckenham | 2024 |
| Catalina Logistics Limited | Coventry | 2023 |
| Catalindan Ltd | Hastings | 2026 |
| Catalloy Limited | Manchester | 1977 |
| Catalogue Returns Park Ltd | Knottingley | 2026 |
| Catalsys Limited | Hartlepool | 2021 |
| Catalyst & Co Corp Ltd | Swindon | 2020 |
| Catalyst CH4NGE Limited | London | 2019 |
| Catalyst Condiments Limited | London | 2020 |
| Catalyst Creative Imaging Limited | West Yorkshire | 1983 |
| Catalyst Engineering Limited | Sutton-In-Ashfield | 2007 |
| Catalyst Europe Ltd | London | 2018 |
| Catalyst Fabrication Services Limited | Northampton | 2023 |
| Catalyst Fuel Ltd | Covent Garden | 2025 |
| Catalyst Human & Business Performance Ltd. | Huddersfield | 2023 |
| Catalyst Media Group Production Ltd | London | 2024 |
| Catalyst Services International Limited | Rugby | 2023 |
| Catalytic Generators UK Limited | London | 2001 |
| Catalytic Support Systems Limited | Runcorn | 1990 |
| Catanitek Ltd | Glasgow | 2024 |
| Catant Ltd | Bradford | 2022 |
| Catapolt Limited | York | 2023 |
| Catapult ERA Jewels Limited | Barking | 2024 |
| Catartes.Aniastudio Limited | Preston | 2023 |
| Catbird Ltd | Wembley | 2011 |
| Catboy Limited | Glasgow | 2011 |
| Catch Life Tackle Ltd | Guisborough | 2026 |
| Catch ME Limited | London | 2025 |
| Catchbadge Ltd | Eastbourne | 2026 |
| Catchcam Technologies Ltd | Cottingham | 2024 |
| Catchco Limited | Bradford | 2025 |
| Catcher and Caught Ltd | Edinburgh | 2026 |
| Catching Light Limited | Stoke-On-Trent | 2016 |
| Catchit Laboratories (UK) Limited | Chelmsford | 2014 |
| Catchlight Media Limited | London | 2011 |
| Catcubcafe Limited | Derby | 2026 |
| Catech. CTS Limited | Hitchin | 2019 |
| Catella Shoemaker Limited | Northampton | 2020 |
| Catena Industries Ltd | Towcester | 2021 |
| Catena Inspection & Engineering Services Limited | Nottingham | 2009 |
| Catena Studios Ltd | Brentwood | 2017 |
| Catenate Industrial Solutions Ltd. | Linlithgow | 2021 |
| Catenate UK Limited | Lancaster | 2008 |
| Cater Care Group Services Limited | Ipswich | 2017 |