| 5-OAKS Television Limited | Crowborough | 2012 |
| 5-STAR Housekeeping Personnel Ltd | London | 2025 |
| 5.9 Cleaning Limited | London | 2025 |
| 5/6 Belmont (Brighton) Limited | Brighton | 2004 |
| 50 Anchors Ltd | Leeds | 2025 |
| 50 CPR Limited | Bristol | 2012 |
| 50 Degrees Limited | Sheffield | 2010 |
| 50 Feet Tall Ltd | London | 2025 |
| 50 Gleneagle Road Management Limited | Norwich | 1973 |
| 50 Harley Street Property Management Limited | Knutsford | 1996 |
| 50 ME 50 YOU Travels Ltd | Hookwood | 2019 |
| 50 Shades of Clean Commercial Ltd | Aberaeron | 2023 |
| 50 Shades of Clean Limited | Aberaeron | 2017 |
| 50 Willes Road Limited | London | 2017 |
| 50-50 Sync CIC | West Drayton | 2011 |
| 50/50 Cars Ltd | Glasgow | 2015 |
| 5000PIECES Ltd | Worthing | 2016 |
| 501 Entertainment Ltd | Aylesford | 2018 |
| 506 Care Ltd | Hull | 2025 |
| 50BY50 CIC | Lichfield | 2025 |
| 50FIFTY Investments Limited | Crawley | 2017 |
| 50TO500 Ltd | London | 2018 |
| 51 Acres Limited | Ruislip | 2007 |
| 51 Belsize Park Gardens Limited | Watford | 2000 |
| 51 Consulting Ltd | London | 2025 |
| 51 Degrees Mobile Experts Limited | Reading | 2009 |
| 51 Frances Road Management Limited | Windsor, Berks | 1979 |
| 51 Moments Ltd | Coventry | 2019 |
| 51 Rippington Drive Limited | Oxford | 2010 |
| 51 Travel Ltd | Huyton | 2023 |
| 51 Warwick Avenue Limited | London | 2006 |
| 51 Whittingstall Road Management Company Limited | Richmond | 2019 |
| 511 Money Transfer Limited | Slough | 2025 |
| 511 Services Ltd | London | 2025 |
| 511 Solutions Ltd | Cambridge | 2025 |
| 513AERO Ltd | Barrow-In-Furness | 2024 |
| 514 Media Ltd | Bourne End | 2017 |
| 515 Limited | Blackpool | 2017 |
| 519 Enforcement Group Ltd | Essex | 2023 |
| 52 Alma Road Management Company Limited | Bristol | 1992 |
| 52 Degrees North Travel Ltd | Stratford-Upon-Avon | 2018 |
| 52 Degrees Northwest Limited | Bolton | 2023 |
| 52 Everything Limited | Wickford | 2024 |
| 52 Gloucester Terrace Management Company (1995) Limited | | 1995 |
| 52 Queens Gardens Management Company Limited | London | 2004 |
| 52 Recruitment Ltd | Blackburn | 2020 |
| 52 ST Johns Villas Limited | London | 2006 |
| 52 Ventures Ltd | Chelmsford | 2026 |
| 525 Selfdrive Ltd | London | 2025 |
| 52EIGHT3 Limited | Hollinwood | 2016 |
| 52J Car Hire Ltd | Stoke On Trent | 2024 |
| 53 Blomfield Road Limited | London | 2015 |
| 53 Edith Road Staff Agency Limited | Northwood Hills | 2024 |
| 53-55A Brackley Road Management Company Limited | Towcester | 2019 |
| 531 Ltd | Southampton | 2006 |
| 532 Services Ltd | Manchester | 2019 |
| 5343 Holdings Ltd | Cardiff | 2012 |
| 535588A Burney Avenue Ltd | Surbiton | 2015 |
| 537 Properties Limited | East Grinstead | 2016 |
| 54 Bishops Avenue Limited | Beaconsfield | 2018 |
| 54 Compayne Gardens Management Company Limited | London | 2015 |
| 54 Devonshire Road Limited | London | 2012 |
| 54 Ditchling Rise Management Limited | Crowborough | 2006 |
| 54 Enforcement Services Ltd | Loughborough | 2026 |
| 54 Exhibitions Ltd | Bristol | 2021 |
| 54 Lascotts Road Limited | Barnet | 2010 |
| 54 MPS Ltd | London | 2020 |
| 54 Penarth Road Management Ltd | Cardiff | 2016 |
| 54 Queen's Gate Holdings Limited | | 2002 |
| 54 Queen's Gate Hotel Nominee 1 Limited | | 2002 |
| 54 Queen's Gate Hotel Nominee 2 Limited | | 2002 |
| 54 Queen's Gate Hotel Property Company Limited | | 2002 |
| 54 Queen's Gate Hotel Reversionary Company Limited | | 2002 |
| 54 Welsh ROW Limited | Nantwich | 2003 |
| 54-56 Percy Road Company Limited | London | 2015 |
| 55 and 46 Degrees North Ltd | Glasgow | 2017 |
| 55 Cancri-E Limited | London | 2014 |
| 55 Clean Ltd | Glasgow | 2025 |
| 55 Exec Search Limited | Letchworth Garden City | 2022 |
| 55 Larkhall Rise Management Company Limited | London | 1997 |
| 55-60 Pilgrim's Reach Management Company Limited | Bristol | 1996 |
| 554 Investments Limited | London | 2024 |
| 555 Cleaning Limited | Seaford | 2019 |
| 555 Sunrise Limited | Birmingham | 2025 |
| 55SE Ltd. | Bradford | 2021 |
| 55THELEMENT Ltd | Merthyr Tydfil | 2025 |
| 55VS HL N1 Limited | Sevenoaks | 2013 |
| 55VS HL N2 Limited | Sevenoaks | 2013 |
| 55VS NO 1 Limited | Sevenoaks | 2013 |
| 55VS NO 2 Limited | Sevenoaks | 2013 |
| 55VS UL N1 Limited | Sevenoaks | 2013 |
| 55VS UL N2 Limited | Sevenoaks | 2013 |
| 56 Black MEN Ltd | London | 2018 |
| 56 Brunswick Gardens Management Limited | London | 1983 |
| 56 C Ltd | Norwich | 2013 |
| 56 Cleaning Limited | Thornton Heath | 2019 |
| 56 Cultural Centre (London) | London | 2025 |
| 56 Fellows Road Limited | London | 2011 |
| 56 Milson Road Limited | London | 2011 |
| 56 North (Scotland) Ltd | Edinburgh | 2017 |