| Castle Blinds Midlands Limited | Derby | 2023 |
| Castle Brewery Ltd | Lostwithiel | 2022 |
| Castle Building Products (Oxon) Limited | Bicester | 2006 |
| Castle Building Services Ltd | Castleford | 2016 |
| Castle Business Forms Limited | Southend On Sea | 1991 |
| Castle Buttons Limited | Corby | 2011 |
| Castle Cafe Knaresborough Ltd | Harrogate | 2023 |
| Castle Carbide Limited | Dudley | 1990 |
| Castle Cartons (Holdings) Limited | Birmingham | 2008 |
| Castle Cartons Limited | Birmingham, | 1970 |
| Castle Cases Ltd | Tamworth | 2011 |
| Castle Catering Engineers Ltd | Nottingham | 2016 |
| Castle Cement Limited | Maidenhead | 1987 |
| Castle Chrome Plating Limited | West Midlands | 2006 |
| Castle Coatings Limited | Caerphilly | 2005 |
| Castle Colour Packaging Limited | Norwich | 1991 |
| Castle Colours Limited | Stoke On Trent | 2020 |
| Castle Commercial Refrigeration Ltd | Paddock Wood | 2014 |
| Castle Composites 2016 Limited | Lanark | 2016 |
| Castle Composites Limited | Lanark | 1998 |
| Castle Concrete Limited | | 1974 |
| Castle Concrete North West Ltd | Clitheroe | 2017 |
| Castle Construction Products Limited | Ilkeston | 2015 |
| Castle Container Services Limited | Derby | 1995 |
| Castle Dairies Limited | Caerphilly | 1986 |
| Castle Dataware Limited | Oakham | 1999 |
| Castle Dental Studio Ltd | Clitheroe | 2012 |
| Castle Design and Printing Ltd | Enfield | 2020 |
| Castle Diamond Technology Limited | Rhyl | 1996 |
| Castle Donington Engineering Limited | Derby | 2008 |
| Castle Doors Ltd | Birmingham | 1996 |
| Castle Eden Fabrications Limited | Hartlepool | 2015 |
| Castle Eden Lift Trucks Limited | Peterlee | 2012 |
| Castle Electrical (Ipswich) Limited | Ipswich | 2013 |
| Castle Electrical Services Limited | Norwich | 2009 |
| Castle Electrodes Limited | Berkshire | 1994 |
| Castle Engineering Co. (Bolsover) Limited | Nottingham | 1988 |
| Castle Engineering Solutions Ltd | Ludlow | 2016 |
| Castle Engravings Ltd | Bedwas | 2025 |
| Castle Enterprises (Midlands) Limited | Warwickshire | 2003 |
| Castle EYE Ltd. | London | 2024 |
| Castle Fabrication & Installation Limited | Seaham | 1994 |
| Castle Fabrication [North East] Limited | Cold Hesledon | 2002 |
| Castle Farm Designs Ltd | Worcester | 2010 |
| Castle Features Joinery Ltd | Exeter | 2025 |
| Castle Fine Arts Foundry Limited | Oswestry | 2002 |
| Castle Footwear Limited | Rochdale | 1999 |
| Castle Fridge Ltd | Paddock Wood | 2014 |
| Castle Glass Limited | Castlederg | 2003 |
| Castle Glen Kitchens Ltd | Castlewellan | 2012 |
| Castle Group Limited | Scarborough | 1989 |
| Castle Group London Ltd | London | 2014 |
| Castle Heat Pumps Ltd | Padock Wood | 2014 |
| Castle Hill Joinery (Ludlow) Limited | Ludlow | 2004 |
| Castle Hill Meats Limited | Saffron Walden | 1999 |
| Castle Hydraulics and Pneumatics Limited | Warwick | 1991 |
| Castle Lighting Limited | Stafford | 1992 |
| Castle Logistics Ltd | London | 2023 |
| Castle M & E Services Limited | Chertsey | 2018 |
| Castle Maclellan Foods Limited | Kirkcudbright | 1982 |
| Castle Manufacturing Limited | Slough | 2020 |
| Castle Marble Limited | Birmingham | 2018 |
| Castle Marine Limited | Caernarfon | 2005 |
| Castle Masonry Products Limited | West Lothian | 2001 |
| Castle Neroche Limited | Park Mansfield | 2003 |
| Castle Paving Products Ltd | Omagh | 2018 |
| Castle Point Iron Works Ltd | Canvey Island | 2020 |
| Castle Polishing & Chrome Plating Limited | Dudley | 2002 |
| Castle Powder Coating Ltd | Leeds | 2014 |
| Castle Print & Design Ltd | Lincoln | 2018 |
| Castle Printwear Ltd | Milford Haven | 2026 |
| Castle Pumps Ltd | Coventry | 2007 |
| Castle Refrigeration (Tonbridge) Limited(The) | Paddock Wood, Tonbridge | 1971 |
| Castle Ribs Ltd | Carmarthen | 2016 |
| Castle Rock Software Ltd | Mildenhall | 2021 |
| Castle Roofline Ltd | Glasgow | 2020 |
| Castle Safe (Holdings) Limited | Shrewsbury | 2013 |
| Castle Scenery Limited | Hungerford | 2026 |
| Castle Sheet Metal Limited | Blackburn | 2003 |
| Castle Shutters Limited | Stevenage | 2013 |
| Castle Spirits Limited | Lancaster | 2023 |
| Castle Steel Services Limited | Kingswinford | 2008 |
| Castle Technical Solutions Limited | Taunton | 2015 |
| Castle Technologies (Stranraer) Limited | Stranraer | 2010 |
| Castle Tees Ltd | South Shields | 2023 |
| Castle Three Motor Company Limited | Alnwick | 2013 |
| Castle Upholstery Limited | Off Jeffreys Road, Enfield | 2006 |
| Castle Vale Displays Limited | Cardiff | 2019 |
| Castle Ventilation Ltd | Carrickfergus | 2020 |
| Castle Ventures Limited | Kettering | 2006 |
| Castle Welding and Fabrication Limited | Glastonbury | 2002 |
| Castle Windows (Midlands) Limited | Lichfield | 2010 |
| Castle Woodworks Limited | Faversham | 2019 |
| Castle Yurts Limited | Hereford | 2008 |
| Castlebroom Engineering Limited | Ipswich | 1985 |
| Castlecraft Sports Ltd. | London | 2025 |
| Castlecrafts Limited | Driffield, | 1954 |
| Castlefield Distillery Limited | Manchester | 2021 |
| Castleford Cooling Services Ltd | Castleford | 2023 |
| Castleford Furniture and Carpet Centre Ltd | Castleford | 2018 |