| 51 Fulham Park Gardens Limited | | 1985 |
| 51 Lillieshall Road Limited | | 1976 |
| 51 Limited | London | 2025 |
| 51 Melrose Avenue Limited | Romford | 2010 |
| 51 North Consulting Limited | Stowmarket | 2009 |
| 51 Sandmere Road Limited | London | 2003 |
| 51 Studio Limited | Ivybridge | 2012 |
| 51% Studios (London) Limited | Bath | 1993 |
| 51.51 Degrees North Limited | Sale | 2014 |
| 510 Wealth (UK) Ltd | Bromley | 2016 |
| 511 Change Consultancy Ltd | Lutterworth | 2022 |
| 511 Engineering Ltd | Wirral | 2019 |
| 512 Consultants Ltd | London | 2022 |
| 512 Design Limited | London | 2021 |
| 513 Inc Ltd | Newton Abbot | 2017 |
| 5143NORTH Limited | Corsham | 2026 |
| 515 North Limited | Dunmow | 2017 |
| 5189 Limited | Newbury | 2021 |
| 519 Consultancy Limited | Salisbury | 2007 |
| 51ST Design Co Ltd | Bridgwater | 2023 |
| 51TOCARBONZERO Limited | Twemlow | 2021 |
| 52 Beverley Road Management Company Limited | Bristol | 2009 |
| 52 Chestnut Grove Management Limited | Liverpool | 2006 |
| 52 Consultancy Limited | Farnham | 2020 |
| 52 Courtfield Gardens Management Company Limited | London | 1978 |
| 52 Degrees North Ltd | Leckhampstead | 2023 |
| 52 Digital Ltd | London | 2018 |
| 52 East Capital Limited | London | 2023 |
| 52 Films Ltd | London | 2018 |
| 52 Gates Consulting Limited | Preston | 2022 |
| 52 Global Consulting Limited | Coventry | 2011 |
| 52 Hackford Road Limited | | 2003 |
| 52 North Health Ltd | Barleythorpe | 2018 |
| 52 ST. Giles Limited | Oxford | 2018 |
| 52 Trafalgar Property Holding Ltd | London | 2023 |
| 524 Taxis Ltd. | Edinburgh | 2020 |
| 525 Accountancy Services Limited | Manchester | 2013 |
| 525 Consulting Ltd | London | 2021 |
| 525 Edin Ltd. | Edinburgh | 2003 |
| 527 Ltd | Hemel Hempstead | 2017 |
| 527869 Limited | | 1954 |
| 528 Limited | Hampstead | 2018 |
| 528 Nation Limited | London | 2022 |
| 5284 Group Limited | Billericay | 2026 |
| 52ART Ltd | York | 2011 |
| 52B.CONSULTING Limited | Yarm | 2015 |
| 52M Consulting Limited | Preston | 2002 |
| 52ND Design Co Ltd | Bridgwater | 2024 |
| 52ND Street Event Solutions Ltd | Barnsley | 2016 |
| 52ND Street Events Supplies Ltd | Barnsley | 2021 |
| 53 Anson Road Limited | South Croydon | 2009 |
| 53 Comeragh Road Limited | | 1994 |
| 53 Degree North Limited | North Yorkshire | 2007 |
| 53 Degrees Accounts Ltd | Nantwich | 2025 |
| 53 Degrees BIM Management Ltd | Thirsk | 2023 |
| 53 Degrees North Engineering Limited | Sheffield | 2013 |
| 53 Degrees North Media Ltd | Chesterfield | 2022 |
| 53 Degrees North UK Limited | Bradford | 2009 |
| 53 Engineering Ltd | Doncaster | 2014 |
| 53 Hampton Road Limited | Bristol | 1989 |
| 53 Quantum Ltd | Swindon | 2005 |
| 53 Queens Gardens Management Company Limited | London | 2004 |
| 53 ST Andrews Road Southsea Management Company Limited | Portsmouth | 2000 |
| 53 Zero Two Ltd | Manchester | 2011 |
| 53/55 Sandy Park Road Management Company Limited | Bristol | 2012 |
| 5302 Consulting Limited | Stockport | 2025 |
| 5311 Ltd | Pershore | 2025 |
| 532MEDIA Limited | London | 2020 |
| 537 Taxis Ltd. | Edinburgh | 2007 |
| 539 Creative Limited | Cullompton | 2014 |
| 53ART Holding Ltd | London | 2022 |
| 53ELEVEN Consulting Limited | Stockport | 2014 |
| 53N Ltd | Wilmslow | 2014 |
| 53RD Consultancy Limited | Greenford | 2025 |
| 53RD Design Co Ltd | Bridgwater | 2024 |
| 53RD Parallel Limited | Ilkley | 2009 |
| 54 Creative Ltd | Telford | 2019 |
| 54 Degrees Design Ltd | Dungannon | 2016 |
| 54 Degrees North Group Ltd | Leeds | 2026 |
| 54 Digital Ltd | Altrincham | 2017 |
| 54 Holmdale Road Limited | London | 1993 |
| 54 Legal Limited | Darlington | 2025 |
| 54 Management Company Limited | Eastbourne | 1998 |
| 54 North Design Ltd | Belfast | 2017 |
| 54 Queensgate Terrace Residents Association Ltd. | London | 1993 |
| 54 Redcliffe Gardens Freehold Limited | | 2008 |
| 54-56 Rewley Road Management Co. Limited | Oxford | 2001 |
| 541 Edin Ltd. | Edinburgh | 2006 |
| 542 Taxis Ltd. | Edinburgh | 2006 |
| 545 Resourcing Ltd | Hook | 2023 |
| 549 Edin Ltd. | Penicuik | 2007 |
| 54LAW.CO.UK Ltd | Sutton Coldfield | 2023 |
| 54XBY Limited | Sutton | 2016 |
| 55 & 55A Queens Road RTM Company Limited | Aldershot | 2011 |
| 55 & 57 ST Nicholas Street Limited | Wadebridge | 1989 |
| 55 and North Limited | Aberdeen | 2019 |
| 55 Connect HR Limited | Weybridge | 2016 |
| 55 Consulting Ltd | Alton | 2024 |
| 55 Degrees Digital Limited | Boldon Colliery | 2025 |
| 55 Degrees Limited | Bath | 2022 |