| Caspara Enterprises Ltd | Middlesbrough | 2025 |
| Caspari Limited | London | 1990 |
| Casperg Group Co., Ltd | Beckenham | 2024 |
| Caspian Filter Technology Ltd | Grimsby | 2004 |
| Caspian Meadow Ltd. | London | 2013 |
| Caspian Metals Ltd | Leeds | 2025 |
| Caspian Semiconductors Limited | Knutsford | 2002 |
| Caspian Tooling & Plastics Ltd | Wallsend | 1994 |
| Casra Consultancy (UK) Limited | Lancashire | 2007 |
| Cass (Scotland) Limited | Isle Of Lewis | 2023 |
| Cass Dayes Ltd | Wallsend | 2018 |
| Cass Engineering Services Ltd | Belfast | 2018 |
| Cass Marine Ltd | Epsom | 2024 |
| Cassandra Novo Ltd | London | 2025 |
| Cassatt Limited | Manchester | 2025 |
| Casscon Limited | Kent | 1981 |
| Casse Limited | Twickenham | 2025 |
| Casse Tete Marine Limited | Hamble | 1993 |
| Cassel ( UK ) Ltd | Dukinfield | 2010 |
| Cassell Welding Ltd | Reading | 2001 |
| Cassia & Sun Ltd | London | 2021 |
| Cassia Chloe Limited | London | 2020 |
| Cassia Contract Manufacturing Limited | | 2002 |
| Cassia Creative Ltd | Glasgow | 2023 |
| Cassia Haze Ltd | London | 2022 |
| Cassidecks Electrical Ltd | Greenock | 2020 |
| Cassidy Systems Limited | Liverpool | 2021 |
| Cassidys Sunblinds Limited | Hull | 2014 |
| Cassie Bespoke Upholstery Limited | Plymouth | 2023 |
| Cassie Essentials Ltd | Doncaster | 2025 |
| Cassie Rose Ltd | Reading | 2021 |
| Cassini Aviation Services Ltd | Cowbridge | 2016 |
| Cassiopeia Globals Ltd | Carshalton | 2025 |
| Cassis Media Ltd | Kew | 2016 |
| Cassius Design Ltd | Watford | 2025 |
| Cassius Fine Joinery Ltd | Leominster | 2018 |
| Cassius Living Limited | Watford | 2018 |
| Cassmax Limited | Northampton | 2025 |
| Casson Validation Solutions Ltd | Ellesmere Port | 2023 |
| Casspea Ltd | London | 2022 |
| Cast Advanced Concretes Holdings Limited | Christchurch | 2017 |
| Cast Advanced Concretes Limited | Christchurch | 2003 |
| Cast Components (UK) Limited | Grantham | 2011 |
| Cast Experience Limited | Sheffield | 2017 |
| Cast Furniture Ltd | Brentwood | 2020 |
| Cast Healthcare Ltd | Draperstown | 2010 |
| Cast Heat Ltd. | Leeds | 1985 |
| Cast Hull Limited | Chesterfield | 1970 |
| Cast in Style Co Ltd | Shifnal | 2002 |
| Cast Iron Brown Ltd | Chichester | 2023 |
| Cast Iron CAD Ltd | Brighton | 2010 |
| Cast Iron Cookers Ltd | Holt | 2014 |
| Cast Iron Fireplace Restorations Ltd | Wilmslow | 2019 |
| Cast Iron Radiators Ltd. | Filey | 2012 |
| Cast Iron Welding Services Limited | Coalville | 1990 |
| Cast LDN Limited | London | 2018 |
| Cast Media Group Limited | Leeds | 1994 |
| Cast Stone (North) Ltd | Newbiggin-By-The-Sea | 2015 |
| Cast Stone Sales and Manufacturing Services Limited | Sandbach | 2024 |
| CAST3D Medical Ltd | Bradford | 2024 |
| Castacrete Limited | Maidstone | 1966 |
| Castalloy Europe Limited | Altrincham | 2016 |
| Castalum Limited | Welshpool | 2008 |
| Castan Cabins Ltd | Llandeilo | 2022 |
| Castbray Limited | Bridgend | 2021 |
| Castco Ltd | Wolverhampton | 2018 |
| Castcom Limited | Broxtowe, Nottingham | 2004 |
| Castec Engineering Ltd | Wrexham | 2025 |
| Castech Refrigeration Ltd | Sevenoaks | 2014 |
| Castelano Ltd | Nottingham | 2023 |
| Castell Gwyn Ltd | Rhyl | 2014 |
| Castell MON Limited | Bangor | 1977 |
| Castell Safety International Limited | London | 1980 |
| Castellex Ltd | Hertford | 2015 |
| Castello Interiors Limited | Middlesbrough | 2021 |
| Castello Luxury Baths Ltd | Westcliff-On-Sea | 2019 |
| Castex Products Limited | High Peak | 1982 |
| Castflow Furnaces Ltd | Bishop Auckland | 2016 |
| Castigliano Limited | London | 1995 |
| Castikipots Limited | Salisbury | 2016 |
| Castilian 1 Ltd | Westhoughton | 2023 |
| Casting & Craft Shop Ltd | Sheffield | 2024 |
| Casting & Process Specialists Limited | Worcester | 2020 |
| Casting Defect Solutions Limited | Peterborough | 2019 |
| Casting Innovations Limited | Rotherham | 2010 |
| Casting Services Engineering Ltd | Leicester | 2016 |
| Casting Support Systems Limited | Paignton | 1994 |
| Castings Promotional Embroidery Limited | Livingston | 2004 |
| Castings Public Limited Company | West Midlands | 1907 |
| Castings Technology International Limited | Rotherham | 2013 |
| Castings Technology Motorsport Ltd | Loscoe, Heanor | 2025 |
| Castironrads Limited | Harrogate | 2010 |
| Castle & Hern Ltd | Newbury | 2025 |
| Castle Acoustics Limited | Hawthorn Park Coal Road | 1973 |
| Castle Air Limited | Liskeard | 1996 |
| Castle Alloys Limited | Wolverhampton | 2026 |
| Castle Alloys Shropshire Limited | Telford | 2025 |
| Castle Architectural Metalwork Ltd | Seaham | 2011 |
| Castle Bake Ltd | Potters Bar | 2026 |
| Castle Blinds & Curtains Ltd | Brierley Hill | 2003 |