| Cassio Mews Two Management Company Limited | Watford | 2003 |
| Cassio Quarter Management Company Limited | Salisbury | 2011 |
| Cassiobury Residential Management Company Limited | Southampton | 2008 |
| Cassland Road Management Company Limited | London | 1999 |
| Castaways Properties Limited | Ulverston | 2023 |
| Castear Residents Association Limited | East Sussex | 1992 |
| Castel Group Ltd | London | 2021 |
| Castell Maen Management Company Limited | New Milton | 2007 |
| Castell Tregrug Management Limited | Usk | 2020 |
| Castellain 25 Limited | London | 2000 |
| Castellain Mansions (East) Limited | Pimlico | 1979 |
| Castellain Mansions (West) Limited | London | 1979 |
| Castellanus Properties Limited | Plymouth | 2024 |
| Castello Services Limited | London | 2009 |
| Castellum Grange (Colchester) Residents Management Company Limited | York | 2020 |
| Castellum House Management Limited | Weybridge | 2024 |
| Castelnau Court Management Limited | London | 1976 |
| Castelnau Gardens RTM Company Limited | London | 2026 |
| Castelnau Property Company Limited | London | 1984 |
| Caster Homes Limited | Luton | 2022 |
| Casterbridge Court (Bournemouth) Limited | Bournemouth | 2003 |
| Casterbridge Court Management Limited | London | 1993 |
| Casterbridge Freehold Company Limited | Templecombe | 2025 |
| Casterbridge Lessees Limited | Croydon | 1999 |
| Casterbridge Place RTM Company Limited | Sherborne | 2024 |
| Casterbridge Property Management Ltd | Ferndown | 2010 |
| Castle & Pavillion Court (Dagenham) Management Company Limited | | 2002 |
| Castle 11/13 Limited | Reading | 2000 |
| Castle Apartments (Bridgwater) Limited | Bridgwater | 2011 |
| Castle Apartments, W-S-M Ltd | Bridgwater | 2013 |
| Castle Approach Management Limited | St Ives | 2015 |
| Castle Avenue Property Management Company Limited | London | 1961 |
| Castle Bar Lodge (Management) Limited | London | 1980 |
| Castle Barns Limited | Kidderminster | 2008 |
| Castle Bay Management Company (Falmouth) Ltd | Redruth | 2010 |
| Castle Brae Management Company Limited | Ballyclare | 2019 |
| Castle Brewery (Newark) RTM Company Limited | Nottingham | 2023 |
| Castle Brewery Management Company Limited | Nottingham | 2002 |
| Castle Camps Management Company Limited | Southend On Sea | 2024 |
| Castle Chambers Limited | Torquay | 2017 |
| Castle Close (Bognor Regis) Residents Association Limited | Bognor Regis | 2021 |
| Castle Close (Eardisley) Residents Association Limited | Hereford | 1996 |
| Castle Close (Sunbury on Thames) Limited | Croydon | 1991 |
| Castle Close Management Company Limited | Gateshead | 1983 |
| Castle Close Residents Association (Orford) Limited | Orford Woodbridge | 1979 |
| Castle Concepts Limited | Yarmouth | 2025 |
| Castle Court (Bolton) Management Company Limited | Bolton | 1991 |
| Castle Court (Dudley) Management Company Limited | Bristol | 2011 |
| Castle Court (Kenilworth) Management Company Limited | Coventry | 1982 |
| Castle Court (Portland) Management Company Limited | Hoddesdon | 2018 |
| Castle Court (Southsea) Management Co. Limited | Portsmouth | 1991 |
| Castle Court (Stogursey) Limited | Stogursey | 1996 |
| Castle Court (Sydenham) Residents Company Limited | Bourne End | 1992 |
| Castle Court (West Kirby) Limited | Wallasey | 1997 |
| Castle Court Apartments (Colne) Limited | Colne | 2003 |
| Castle Court Helmsley Limited | Ilkley | 1997 |
| Castle Court Management (Keighley) Company Limited | Settle | 1964 |
| Castle Court Management (Shirley) Limited | Poole | 1991 |
| Castle Court Management Limited | Northampton | 1984 |
| Castle Court Northern RTM Company Limited | York | 2017 |
| Castle Court Residents Association (Stroud) Limited | Cheltenham | 1988 |
| Castle Court Residents Association Limited | Aylesbury | 1969 |
| Castle Court RTM Company Limited | Bournemouth | 2018 |
| Castle Court Southern RTM Company Limited | York | 2017 |
| Castle Court Western RTM Company Limited | York | 2017 |
| Castle Courtyard Limited | Plympton | 2017 |
| Castle Courtyard Management Company Limited | Sheffield | 2022 |
| Castle Croft (Barnard Castle) Management Company Limited | Tarporley | 2018 |
| Castle Croft Drive Management Company Limited | Limavady | 2019 |
| Castle Croft, Bridge Street Management Company Limited | Swadlincote | 2002 |
| Castle Crown Properties Limited | Bedale | 2014 |
| Castle Developments Limited | Winchester | 1987 |
| Castle Donington Residents Management Company Limited | Derby | 2019 |
| Castle END Management Company Limited | Huntley | 2021 |
| Castle Erin Management Company Ltd | Limavady | 2023 |
| Castle Estates (Hallam) Limited | Rotherham | 2002 |
| Castle Farm Eardisley Limited | Hereford | 1993 |
| Castle Fields (Ewloe Green) Management Company Limited | Wilmslow | 2014 |
| Castle Foundry Management Limited | Penrith | 2011 |
| Castle Freehold (Colchester) Limited | Colchester | 2026 |
| Castle Garden Freehold Limited | Horndean | 2002 |
| Castle Gardens (Management) Limited | Colchester | 2002 |
| Castle Gardens Residents Association Limited | Bexhill-On-Sea | 2009 |
| Castle Gardens Tenants Association Ltd | Midhurst | 2013 |
| Castle Gate (Bedford) Ltd | Leighton Buzzard | 2025 |
| Castle Gate Marlborough Way Management Company Limited | Shrewsbury | 2008 |
| Castle Glen Management Co. Ltd | Hythe | 1997 |
| Castle Grange (Pontefract) Management Company Limited | Leeds | 2005 |
| Castle Green (Dagenham) Management Company Limited | Kent | 1989 |
| Castle Green (Holt) Residents Management Company Limited | Tarporley | 2020 |
| Castle Green (Shotton) Management Company Limited | Durham | 2013 |
| Castle Green Residents Management Company Limited | Birmingham | 2025 |
| Castle Group Management Ltd | Windsor | 2019 |
| Castle Grove (Oldbury) Management Ltd | Oldbury | 2023 |
| Castle Grove (Pontefract) Management Company Limited | Salisbury | 2004 |
| Castle Grove Management Company Limited | Taunton | 2020 |
| Castle Heights (Lynton) Limited | Barnstaple | 2009 |
| Castle Heights Court Limited | Farnham | 1992 |
| Castle Heights Management (Southampton) Limited | Southampton | 1999 |
| Castle Heights Management Limited | Scarborough | 2006 |