| Iron Horse Motor Lines Limited | Other services | 2018 |
| Iron Ventures Limited | Professional & scientific | 2026 |
| Irons Court Management Ltd | Households | 2020 |
| Isis Fluid Holdings Limited | Financial services | 2020 |
| Iterra Studio Ltd | Wholesale & retail | 2025 |
| IVY T Limited | Wholesale & retail | 2017 |
| IW Consultancy Limited | Information & communication | 2002 |
| Iwgc Limited | Information & communication | 2008 |
| Izzysolutions Ltd | Public administration | 2025 |
| J a Joinery & Carpentry Ltd | Construction | 2014 |
| J P Hames Limited | Administrative & support | 2022 |
| J. Ford Plumbing & Heating Limited | Construction | 2002 |
| Jade Ellery Dressage Ltd | Agriculture & fishing | 2021 |
| Jaffe and Neale Limited | Wholesale & retail | 2011 |
| Jake Morant Properties Ltd | Real estate | 2023 |
| JAM & Partners Limited | Professional & scientific | 2014 |
| James Collington Personal Training Limited | Arts & recreation | 2013 |
| James Golden Consultancy Ltd | Professional & scientific | 2022 |
| James Mackintosh Architects Limited | Professional & scientific | 2017 |
| James Monro Executive Resourcing Ltd | Administrative & support | 2007 |
| Jamestown Mills Ltd | Real estate | 2016 |
| Jami Associates Limited | Information & communication | 2001 |
| JC Wine Events Ltd | Wholesale & retail | 2010 |
| JCM Health Limited | Health & social care | 2006 |
| Jenivision Ltd | Information & communication | 2026 |
| Jericho Writers Ltd | Information & communication | 2023 |
| JF Gardens Limited | Administrative & support | 2023 |
| JG RE Advisors Limited | Real estate | 2024 |
| Jilly's Properties Ltd | Real estate | 2025 |
| Jilly's Property Ltd | Households | 2025 |
| JJ Manufacturing Limited | Wholesale & retail | 2024 |
| JLC Cocktails Limited | Hospitality | 2024 |
| Jnash Software Consultancy Ltd | Administrative & support | 2016 |
| JOE Public London Ltd | Professional & scientific | 2024 |
| Joel and Frazer Productions Ltd | Information & communication | 2024 |
| Johnston Estate Management Group Limited | Administrative & support | 2016 |
| Johnston Quarry Group Limited | Mining & quarrying | 2007 |
| Joinery Studio Ltd | Information & communication | 2022 |
| Jonathan Uglow Garden Design Limited | Professional & scientific | 2019 |
| Jordan Hennessy Asset Management Limited | Financial services | 2013 |
| JRN Properties (Chipping Norton) Ltd | Real estate | 2022 |
| JTR Rigging Ltd | Manufacturing | 2014 |
| Jujujaan Ltd | Arts & recreation | 2022 |
| Jussabs & Associates Ltd | Wholesale & retail | 2020 |
| JV Noble GAS & Heating Engineering Ltd | Energy | 2022 |
| K Lamb Associates Ltd | Professional & scientific | 2016 |
| K.J. Millard Limited | Administrative & support | 1984 |
| Kaduna Foods Ltd | Wholesale & retail | 2014 |
| Kala Trading Limited | Wholesale & retail | 2020 |
| Kangakan Ltd | Wholesale & retail | 2022 |
| Karazan Ltd | Hospitality | 2024 |
| Karers 4 Kidz | Health & social care | 2005 |
| Karindell Limited | Real estate | 1994 |
| Karrek Limited | Real estate | 2024 |
| Kastle Resources Limited | Professional & scientific | 1986 |
| Katharos Asset Holdco 1 Limited | Construction | 2025 |
| Katharos Asset Holdco 2 Limited | Construction | 2025 |
| Katharos Infrastructure Investments Limited | Financial services | 2024 |
| Katharos Projectco SPV 1 Limited | Construction | 2025 |
| Katherine Barclay Limited | Professional & scientific | 2004 |
| Kathy Thompson Learning and Coaching Ltd | Professional & scientific | 2019 |
| Kavitat Ltd | Construction | 2024 |
| Kenika Limited | Real estate | 1999 |
| Kethero Management Company Limited | Households | 2016 |
| Keystone Therapies Ltd | Professional & scientific | 2011 |
| Kindred Workplace Design & Strategy Ltd | Professional & scientific | 2024 |
| King Stone Distillery Ltd | Manufacturing | 2019 |
| Kingham House Management Company Limited | Real estate | 2007 |
| Kirmada Ltd | Information & communication | 2020 |
| Kitty's House Limited | Real estate | 2025 |
| Klearview Consultancy Limited | Financial services | 2024 |
| Kneadwise Massage Ltd | Other services | 2021 |
| Knight Land Brokers Ltd | Real estate | 2025 |
| Kopyrite Limited | Administrative & support | 2011 |
| LA Source SKI & Adventure Limited | Hospitality | 1998 |
| LAB133 Ltd | Arts & recreation | 2007 |
| Ladyfield Renewable Energy Park Ltd | Energy | 2021 |
| Landsdown Capital Ltd | Real estate | 2011 |
| Langtons Consultancy Limited | Professional & scientific | 2024 |
| LAP Family Investment Co Limited | Financial services | 2025 |
| Lara Way Designs Ltd | Professional & scientific | 2025 |
| Laurence Vaughan Limited | Financial services | 2013 |
| Lawrence Home Nursing Team Ltd | Health & social care | 2020 |
| LB Acupuncture Limited | Health & social care | 2024 |
| Leave IT to US Limited | Administrative & support | 2019 |
| Legard & Cashell Holdings Ltd | Real estate | 2017 |
| LEO and the Duck Limited | Wholesale & retail | 2020 |
| LEO Paper Products (UK) Limited | Manufacturing | 2000 |
| Libby Robok Limited | Professional & scientific | 2022 |
| Lidar Tech UK Ltd | Wholesale & retail | 2023 |
| Lightway Plumbing & Heating Ltd | Construction | 2020 |
| List Logic Limited | Information & communication | 2008 |
| Little Garden Wood Limited | Agriculture & fishing | 2007 |
| Living Eyes Ltd | Real estate | 2024 |
| LIZ Fensome Design Ltd | Professional & scientific | 2018 |
| Lloyd Charles Installations Limited | Construction | 2015 |
| Local Authority Consultancy Services Limited | Administrative & support | 1983 |
| Loedan Leadership Limited | Professional & scientific | 2026 |
| Logue & SON Limited | Construction | 2011 |
| London Waterloo Hostel Limited | Extraterritorial | 2017 |