| Castle Mortgage Advice Ltd | Edinburgh | 2018 |
| Castle Mortgage Solutions Ltd | Alnwick | 2022 |
| Castle Mortgages Limited | Kenilworth | 2026 |
| Castle Nursery (Bromsgrove) Limited | Stourbridge | 2010 |
| Castle Operations Ltd | Edinburgh | 2010 |
| Castle Paving Northern Ireland Ltd | Omagh | 2014 |
| Castle Payroll Consulting Limited | Biggleswade | 2018 |
| Castle Pharma Holdings Ltd | Belfast | 2024 |
| Castle Phillips (Holdings) Limited | Woking | 1968 |
| Castle Phillips Finance Company Limited | Woking | 1971 |
| Castle Portcullis Holdings Limited | Derby | 2025 |
| Castle Portfolio 1 Limited | Runcorn | 2025 |
| Castle Property Holding Group Limited | London | 2021 |
| Castle Property Investments Limited | Berkhamsted | 2022 |
| Castle Property Services Holdings Limited | Newcastle Under Lyme | 2016 |
| Castle Residential Holdings Limited | Woking | 2017 |
| Castle Rigby Ltd | London | 2018 |
| Castle Road Mortgages Ltd | Bedford | 2025 |
| Castle Rock Capitals Ltd | London | 2024 |
| Castle Rock Commercial Finance Ltd | Nottingham | 2024 |
| Castle Rock Financial Planning Ltd | Nottingham | 2019 |
| Castle Rock Limited | Ashton-Under-Lyne | 2025 |
| Castle Safety & Risk Services Ltd | Barnard Castle | 2017 |
| Castle Sheet Holdings Ltd | Langho, Blackburn | 2026 |
| Castle Square Holdings Limited | Sheffield | 2019 |
| Castle Stonebridge Limited | Chesterfield | 2021 |
| Castle Sundborn Limited | Malmesbury | 1964 |
| Castle Top Holding Limited | London | 2019 |
| Castle Tower Mortgages Limited | Newcastle Upon Tyne | 2025 |
| Castle Trust Capital PLC | London | 2010 |
| Castle Trust Holdings Limited | London | 2019 |
| Castle Trust POS Limited | London | 2016 |
| Castle UK Bidco Limited | Derby | 2021 |
| Castle UK Midco 1 Limited | Derby | 2022 |
| Castle UK Midco 2 Limited | Derby | 2021 |
| Castle Vehicle Leasing Holdings Limited | Shoreham-By-Sea | 2013 |
| Castle Venture Holdings Limited | Fareham | 2020 |
| Castle View Chepstow Holdings Limited | Chepstow | 2019 |
| Castle View Finance Limited | Carlisle | 2021 |
| Castle View Group Ltd | Bonnyrigg | 2024 |
| Castle View Holdings Ltd | Bonnyrigg | 2024 |
| Castle View Nursery Holdings Limited | Loughbrough | 2020 |
| Castle View Property Finance Ltd | Carlisle | 2023 |
| Castle Wealth International Ltd | Liverpool | 2022 |
| Castleacre Insurance Services Ltd | Ipswich | 2004 |
| Castlebank Capital Limited | Macclesfield | 1988 |
| Castlebar Management Limited | London | 1985 |
| Castlebay Ltd | Glasgow | 2023 |
| Castleblair Group Ltd | Dunfermline | 2020 |
| Castlebridge Finance Limited | Bristol | 2020 |
| Castlebridge Holdings Limited | Bromley | 1986 |
| Castlebridge Risk Solutions Ltd | Cardiff | 2025 |
| Castlebridge RX SPV Ltd | Bristol | 2023 |
| Castlebridge SPV Limited | Bristol | 2020 |
| Castlebrooke Limited | Windsor | 2016 |
| Castlecarney Limited | Dungannon | 2023 |
| Castlecourt Group Ltd | Wigan | 2025 |
| Castledene Amey Holdings Limited | Aylesford | 2021 |
| Castlederry Financial Consultants Limited | Shaftesbury | 2008 |
| Castledine Driving Force Limited | Derby | 1988 |
| Castledine Holdings Ltd | Bexhill-On-Sea | 2025 |
| Castlefield Advisory Partners Limited | Manchester | 2008 |
| Castlefield Capital Partners Ltd | Wickford | 2021 |
| Castlefield Holdings Limited | Manchester | 2015 |
| Castlefield Partners Limited | Manchester | 2009 |
| Castleford JV Holdings Limited | Castleford | 2017 |
| Castlefort Limited | London | 2023 |
| Castlegate 730 Limited | London | 2014 |
| Castlegate 755 Limited | Derby | 2016 |
| Castlegate 788 Limited | Stockton Heath | 2020 |
| Castlegate Capital Limited | Nottingham | 2016 |
| Castlegate Financial Management Limited | Lincolnshire | 1986 |
| Castlegate Pension Administration Limited | Lincolnshire | 2001 |
| Castlegate Union Limited | Edinburgh | 2019 |
| Castlegate Wealth (Holdings) Limited | Grantham | 1998 |
| Castlehaven Investments Limited | Milton Keynes | 2019 |
| Castlehaven SPV 7 Limited | London | 2025 |
| Castlehaw Limited | Sedbergh | 2017 |
| Castlehill Pension Trustees Limited | Londonderry | 2021 |
| Castlelake Holdings (UK) Limited | London | 2006 |
| Castlelaurie Investments Limited | London | 2013 |
| Castleline Holdings Limited | Pontypridd | 2024 |
| Castlemaine Affiliates Ltd | Lincoln | 2021 |
| Castleman Commercial Ltd | Loughborough | 2026 |
| Castleman Mortgages Limited | Loughborough | 2022 |
| Castlemead Holdings Limited | Bristol | 2019 |
| Castlemead Insurance Brokers Limited | Bristol | 1987 |
| Castlemere Developments Limited | Windsor | 2017 |
| Castlemere Holdings Limited | Windsor | 2017 |
| Castlemoon Europe Limited | Bath | 2015 |
| Castlemore Homes Group Limited | Gerrards Cross | 2021 |
| Castleplus Limited | Mayfair | 2009 |
| Castleplus Properties Limited | Mayfair | 2013 |
| Castlereagh Properties Limited | Belfast | 2003 |
| Castlerock Holiday Parks Holdings Ltd | Coleraine | 2025 |
| Castlerock Wealth Management Limited | Rochester | 2014 |
| Castleroy Ltd | London | 2025 |
| Castles Group Ltd | Waltham Cross | 2021 |
| Castles Holdings Ltd | New Milton | 2023 |
| Castles Property Group Ltd | Hemel Hempstead | 2024 |