| Castle HEY Management Co. Limited | Manchester | 2005 |
| Castle Hill (Bardsey) Management Limited | Leeds | 2004 |
| Castle Hill (Barratt) Residents Management Company Limited | Hoddesdon | 2016 |
| Castle Hill (Cottingham) Management Company Limited | York | 2018 |
| Castle Hill (DWH1) Residents Management Company Limited | Hoddesdon | 2017 |
| Castle Hill (Saffron Walden) Management Co. Limited | Saffron Walden | 1973 |
| Castle Hill Court (Berkhamsted) Management Limited | Berkhamsted | 1975 |
| Castle Hill Court (Folkstone) Limited | Folkestone | 1995 |
| Castle Hill Court (Parkstone) Limited | Poole | 1975 |
| Castle Hill Court (Prestbury) Ltd | Macclesfield | 2010 |
| Castle Hill Court (ST. Fagans) Maintenance Limited | Cardiff | 1969 |
| Castle Hill Court Management Company Limited | Redruth | 1987 |
| Castle Hill House (Parkstone) Limited | Bourne End | 2018 |
| Castle Hill House Management Co Limited | Walkden | 2021 |
| Castle Hill Management Limited | Dorchester | 1995 |
| Castle Hill Residents Association Limited | Camberley | 1992 |
| Castle Holdings Property Management Ltd | Moira | 2025 |
| Castle House (Axminster) Management Company Limited | Axminster | 1996 |
| Castle House (Hertford) Management Limited | Hatfield | 2019 |
| Castle House (High Wycombe) Management Company Limited | Southend-On-Sea | 2018 |
| Castle House Flats Management Company Limited | London | 2000 |
| Castle House Hastings Limited | Brighton | 2000 |
| Castle House Management Company (East Street Tonbridge) Limited | Tonbridge | 2016 |
| Castle House Management Group Ltd | Norwich | 2026 |
| Castle House Management Limited | Newbury | 1987 |
| Castle House Residents Management Company Limited | Hornchurch | 2003 |
| Castle Housing Solutions Ltd | Rochdale | 2025 |
| Castle Hurst (Amenities) Limited | Robertsbridge | 1986 |
| Castle Inn Apartments Limited | Coalville | 2018 |
| Castle Irwell Management Company Limited | Manchester | 2021 |
| Castle Keep (Northwich) Management Company Limited | Chester | 2005 |
| Castle Keep (Reigate) Property Management Company Limited | Whyteleafe | 1999 |
| Castle Keep (Wetherby) Management Company Limited | York | 2005 |
| Castle Keep Estate Management Limited | Bedford | 1994 |
| Castle Keep Homes Ltd | Swansea | 2026 |
| Castle Keep Launceston RTM Company Limited | Liskeard | 2021 |
| Castle Keep Management Company Limited | Liverpool | 1984 |
| Castle Kimberley Property Limited | Bournemouth | 2018 |
| Castle Lane East Limited | Christchurch | 2013 |
| Castle Letting Agency Ltd | Strathaven | 2018 |
| Castle Linn Management Limited | Portstewart | 2019 |
| Castle Lodge 1805-2021 Management Company Limited | London | 2020 |
| Castle Lodge Management Company Limited | Wokingham | 1983 |
| Castle Maltings Stansted Management Company Limited | Bishop Stortford | 2016 |
| Castle Management Company Limited(The) | Stroud | 1982 |
| Castle Manor & Ashby Fields Management Company Limited | Cambridge | 2023 |
| Castle Manor Estate Management Ltd | Gilford | 2017 |
| Castle Marina Residents Association Limited | Cambridge | 1987 |
| Castle Meadow (Management Company) Limited | Cambridge | 2021 |
| Castle Meadows (Tamworth) Management Limited | Swadlincote | 2003 |
| Castle Meadows (Telford) Management Company Limited | New Milton | 2008 |
| Castle Meadows Court Limited | St. Agnes | 1977 |
| Castle Meadows Management Company Limited | Windermere | 1997 |
| Castle Mews (Beccles) Limited | Beccles | 2019 |
| Castle Mews (Caerphilly) Management Company Limited | Bourne End | 2006 |
| Castle Mews (Hertford) Management Company Limited | Nazeing | 2020 |
| Castle Mews (Pontefract) Management Company Limited | Salisbury | 2006 |
| Castle Mews (Shrewsbury) Management Company Limited | Croydon | 2002 |
| Castle Mews (Trowbridge) Management Company Limited | Frome | 2002 |
| Castle Mews (Weybridge) Residents Management Company Limited | Staines-Upon-Thames | 2006 |
| Castle Mews Berkhamsted Limited | Shrewsbury | 2002 |
| Castle Mews Caerleon Management 1990 Limited | Newport | 1991 |
| Castle Mews Homes Limited | Stafford | 2010 |
| Castle Mews Limited | Whitehaven | 1990 |
| Castle Mews Management (NO.1)LIMITED | Ballygowan Road | 1987 |
| Castle Mews Management (NO.2) Limited | Newtownards | 1987 |
| Castle Mews Management Company (Horndean) Limited | Liphook | 2008 |
| Castle Mews Management Company (Rayleigh) Limited | Southend-On-Sea | 1998 |
| Castle Mews Management Company Limited | Upham, Southampton | 1990 |
| Castle Mews Newark (Residents) Management Limited | Shrewsbury | 1990 |
| Castle Mews Residents Management Company Limited | Southampton | 2007 |
| Castle Mews Tonbridge Management Company Limited | Gravesend | 2022 |
| Castle Mill Apartments Limited | Harpenden | 2005 |
| Castle Mills (Melbourne) Residents Limited | Swadlincote | 1992 |
| Castle Mills Dromore Limited | Newry | 2006 |
| Castle Mills Management Company Limited | Knaresborough | 1987 |
| Castle Mount Mirfield Management Company Limited | Mirfield | 2014 |
| Castle Oaks (Parkhill) Management Limited | Bromley | 1975 |
| Castle Park (Wallingford) Company Limited | Witney | 1997 |
| Castle Park (West Durrington) Management Company Limited | New Milton | 2021 |
| Castle Place Bletchingley Freehold Ltd | Redhill | 2013 |
| Castle Place Bletchingley Management Limited | Redhill | 2025 |
| Castle Place Freehold Limited | Sevenoaks | 2013 |
| Castle Place Management Company Limited | Camberley | 1999 |
| Castle Point (Nottingham) Management Limited | Cambridge | 2014 |
| Castle Point Management (Hinckley) Limited | Hinckley | 2005 |
| Castle Pond Management Company Limited | Essex | 2003 |
| Castle Quay (Neath) Management Limited | Neath | 1993 |
| Castle Quay Management Limited | Hemel Hempstead | 2006 |
| Castle Quay Mews Limited | Colwyn Bay | 2002 |
| Castle Quay Property Management Limited | Loughborough | 1989 |
| Castle Quays Limited | Tyne & Wear | 1994 |
| Castle Reach (King's Lynn) Management Company Limited | Norwich | 2025 |
| Castle Rigg Access Management Limited | Ponteland | 2025 |
| Castle Rise (Flats) Management Ltd | Stroud | 2023 |
| Castle Road (Wakefield) Management Limited | Wakefield | 2007 |
| Castle Road (Whitstable) Flats Limited | Whitstable | 1974 |
| Castle Rock Management Company Limited | Wadebridge | 2005 |
| Castle Square (Ludlow) Residents Limited | Ludlow | 2008 |
| Castle ST George Management (NO.1) Limited | Weston Super Mare | 1991 |