| Castle Foods Ltd | Galston | 2008 |
| Castle Galleries Retail Limited | Birmingham | 2009 |
| Castle Gate Apartments NO. 1 Limited | Bangor | 2008 |
| Castle Group Pension Trustees Limited | Bedford | 2017 |
| Castle Hall Management Company Limited | Milford Haven | 2021 |
| Castle Hill 165 Limited | Brierley Hill | 2015 |
| Castle Hill Dudley Limited | London | 2005 |
| Castle Hill Holdings Limited | Lincoln | 1963 |
| Castle Hill Services Company (NI) Ltd | Castlewellan | 2006 |
| Castle Hills Eaton Socon Management Company Limited | Spalding | 2004 |
| Castle House Collection Limited | Englefield Green | 2025 |
| Castle House Hotel Limited | Hereford | 1995 |
| Castle Island Holdings (2) Limited | Salford | 2022 |
| Castle Island Holdings Limited | Salford | 2022 |
| Castle Janitorial Ltd | Skipton | 2023 |
| Castle Keep Geospatial Ltd | Co Durham | 2022 |
| Castle Keep Utilities Ltd | Co Durham | 2022 |
| Castle Lift Trucks Limited | Basingstoke | 1987 |
| Castle Lodge Apartments Limited | Bangor | 1999 |
| Castle Meadow Consultancy Ltd | Norwich | 2021 |
| Castle Mews Management Company (Graveney Road) Limited | London | 2003 |
| Castle Minibus Limited | Shoreham By Sea | 2013 |
| Castle Motor Company Limited | Liskeard | 2009 |
| Castle Muerau Ltd | St. Neots | 2020 |
| Castle Newsagents Ltd | Glasgow | 2009 |
| Castle Park Theatre CIC | Colchester | 2021 |
| Castle Pets Bedfordshire Limited | Bedford | 2017 |
| Castle Point Building Supplies Ltd | Benfleet | 2017 |
| Castle Point Reclaim Ltd | Benfleet | 2017 |
| Castle Point Skips Limited | Benfleet | 2012 |
| Castle Point Timber Supplies Ltd | Benfleet | 2017 |
| Castle Premier Services Limited | Shoreham-By-Sea | 2013 |
| Castle Property Contractors Limited | Wolverhampton | 2009 |
| Castle Rock Brewery Ltd | Nottingham | 1997 |
| Castle Smart Homes Ltd | Nottingham | 2024 |
| Castle Street Nominees Limited | Edinburgh | 1972 |
| Castle Street Nominees UK Limited | Oxford | 2014 |
| Castle Tapes and Industrial Solutions Limited | Walsall | 2018 |
| Castle Trinity Limited | Leeds | 2017 |
| Castle Van Hire Ltd | Warwick | 2025 |
| Castle Vehicle Leasing Limited | Shoreham By Sea | 2023 |
| Castle Vending | Craigavon | 2013 |
| Castle Vets Pet Healthcare Limited | Bristol | 2011 |
| Castle View 1960 Limited | Chesterfield | 2014 |
| Castle Walk Reigate Limited | Worthing | 2008 |
| Castle Wealth Management Ltd | Great Chesterford | 2019 |
| Castlechime Limited | London | 2006 |
| Castlecraft Innovations Ltd | London | 2026 |
| Castlederg Green Management Co Limited | Claudy | 2007 |
| Castlefield Products Limited | Stourbridge | 2007 |
| Castlefield Secretaries Limited | Manchester | 1996 |
| Castlefield Wealth Management Limited | Manchester | 2007 |
| Castleford Car Centre Limited | Goole | 2017 |
| Castlegate 123 Limited | Brackley | 2015 |
| Castlegate 143 Limited | Nottingham | 1946 |
| Castlegate 511 Limited | Amotherby | 2008 |
| Castlegate Business Park (Salisbury) Limited | Salisbury | 2013 |
| Castlemeadow Homes Ltd | Dereham | 2005 |
| Castlereagh Investments Limited | Belfast | 2005 |
| Castlestreet Farming Limited | Georgeham | 2015 |
| Castleton 1965 Limited | Scunthorpe | 2014 |
| Castleton Property Company Limited | 1 Hawksworth Street | 2012 |
| Castletown Berehaven Holdings Limited | Strabane | 2021 |
| Castletown Trading Company Ltd. | Taunton | 2000 |
| Castleviewuk Forensics Limited | Holmfirth | 2008 |
| Castlewich Estates Limited | Saltash | 2008 |
| Castlewigg Gwynne Limited | Newton Stewart | 2014 |
| Castlewood Court Management Ltd | Belfast | 2009 |
| Castlewood Manor Apartments Limited | Belfast | 1999 |
| Castlewood N16 Limited | London | 2004 |
| Castor Island Ltd | Thornton Heath | 2021 |
| Castpine Limited | Bridgend | 2026 |
| Castrejo Ltd | Andover | 2018 |
| Castro Music Ltd | Cardiff | 2017 |
| Caststitch Holdings Limited | Congleton | 2001 |
| Casual Finance Ltd | Brentwood | 2012 |
| Casual Terrace Wear UK Ltd | County Durham | 2020 |
| Casuall Fashion Co., Ltd | Manchester | 2019 |
| Cat 20 Ltd | Birmingham | 2017 |
| Cat of the EYE Ltd | Manchester | 2025 |
| Cat Productions Ltd | London | 1994 |
| Cat Techs Ltd | Scunthorpe | 2009 |
| Cataland Ltd | Liverpool | 2014 |
| Catalco Limited | Widnes | 2015 |
| Catalina & Associates Ltd | Beckenham | 2020 |
| Catalina Bay Limited | Enniskillen | 2009 |
| Catalis Group Limited | Croydon | 1998 |
| Catalogue Ltd | Saffron Walden | 1993 |
| Catalogue Returns Ltd | Knottingley | 2015 |
| Catalpa IT Limited | Newbury | 2014 |
| Catals Investment Ltd | London | 2025 |
| Catalysis Management Ltd | Royston | 2002 |
| Catalyst Enterprise Consultants Limited | Abergavenny | 1992 |
| Catalyst Environmental Limited | London | 2007 |
| Catalyst for International Services Limited | Manchester | 2026 |
| Catalyst Global Music Limited | London | 2012 |
| Catalyst Link Ltd | London | 2025 |
| Catalyst Realm for Investment Ltd | Manchester | 2025 |
| Catalyst-Red Ltd | Stamford | 2006 |
| Catalytica Ltd | Whitegate | 2019 |