| Joy & Co Secretary Services Limited | Extraterritorial | 2007 |
| Joyland Limited | Real estate | 2001 |
| JPB Systems Co. Limited | Information & communication | 1995 |
| JPD Drylining | | 1995 |
| JPF Maintenance Services Ltd | Energy | 2017 |
| JPG Perfect Ltd | Construction | 2023 |
| JRC Maintenance Limited | Construction | 1999 |
| JRM Construction Limited | Construction | 2007 |
| JRS Distribution Ltd | Wholesale & retail | 2024 |
| Jsc(Uk) Ltd | Construction | 2016 |
| Jscreps Ltd | Wholesale & retail | 2021 |
| JSD Legal Limited | Professional & scientific | 2026 |
| JSE Consulting Limited | Information & communication | 2006 |
| JSG Architectrual Systems & Hardware Ltd | Construction | 2020 |
| JSM Associates (LON) LLP | | 2016 |
| Jsmj Limited | Professional & scientific | 2007 |
| JSN Store X Ltd | Wholesale & retail | 2024 |
| JSP Properties Holdings Ltd | Real estate | 2024 |
| Jssd Constructions Ltd | Construction | 2017 |
| Jteco Ltd | Construction | 2025 |
| Jtecsol Limited | Wholesale & retail | 2004 |
| Jugunoo Ltd | Wholesale & retail | 2025 |
| Jules Medico-Legal Services Limited | Administrative & support | 2025 |
| Julia Korper Interior Design Limited | Administrative & support | 1989 |
| Julian Financial Services Limited | Extraterritorial | 2007 |
| Julikay UK Limited | Health & social care | 2016 |
| Julius Nielsen (UK) Limited | Professional & scientific | 2002 |
| Jumbo Developments Limited | Construction | 2006 |
| Junrian Limited | Other services | 2007 |
| Junz Limited | Information & communication | 2025 |
| Jupiter Training Limited | Information & communication | 2001 |
| Jurassic Cottage Ltd | Wholesale & retail | 2013 |
| Jurfipadin Ltd | Information & communication | 2026 |
| JUS4US Limited | Real estate | 2003 |
| Just ASK Training Ltd | Administrative & support | 2021 |
| Just Buy IT Mate Ltd | Wholesale & retail | 2025 |
| Just Develop Ltd | Real estate | 2019 |
| Just FUN Ltd | Education | 2002 |
| Just Miles Ltd | Wholesale & retail | 2020 |
| Just One TEE CES Limited | Wholesale & retail | 2025 |
| Just Passing School of Motoring Ltd | Education | 2007 |
| Juta Limited | Construction | 2007 |
| JVC Leisure Limited | Arts & recreation | 1997 |
| JWB Trading Ltd | Wholesale & retail | 2020 |
| Jxsi Trading Co., Ltd | Wholesale & retail | 2023 |
| Jymi Properties Ltd | Real estate | 2025 |
| JZ Homes Ltd | Real estate | 2026 |
| K & a Direct Limited | Construction | 1998 |
| K & K Mortgage Solutions Ltd | Financial services | 2007 |
| K & M Art Supplies Limited | Wholesale & retail | 2007 |
| K E Kents Holdings Limited | Professional & scientific | 2006 |
| K Knowlden Limited | Manufacturing | 2005 |
| K W Clarke (Foam) Limited | | 1964 |
| K Wallis & Sons Limited | Construction | 2003 |
| K&M Mcloughlin Decorating Schools Community Interest Company | Education | 2014 |
| K.A.Y.A Organisations Ltd | Education | 2024 |
| K.C. Improvements Limited | Construction | 2004 |
| K.C. Smith Limited | Administrative & support | 2003 |
| K.E. Kents Limited | Transport & logistics | 1998 |
| K.I.M. Business Services Limited | Professional & scientific | 1996 |
| K.J. Electrical (Ingatestone) Limited | Wholesale & retail | 1974 |
| K.R.H. (Building Services) Limited | Construction | 2003 |
| K.R.K. Marine & Liquid Logistics (UK) Limited | Wholesale & retail | 2026 |
| K.S.K. Properties Limited | Real estate | 1994 |
| K2M2 Properties Ltd | Construction | 2026 |
| Kabel CLO Limited | Wholesale & retail | 2025 |
| Kade Computers Limited | | 1985 |
| Kaelis Partners Ltd | Wholesale & retail | 2026 |
| KAF Telecom Ltd | Information & communication | 2014 |
| KAH UK Ltd | Wholesale & retail | 2018 |
| Kahaf Ltd | Wholesale & retail | 2021 |
| Kairo's Vegan Sweets Ltd | Wholesale & retail | 2024 |
| Kaizen RYU Karate Limited | Arts & recreation | 2000 |
| Kaizen RYU UK Limited | Arts & recreation | 2006 |
| Kaizen VIP Ltd | Professional & scientific | 2024 |
| Kajagoogoo Limited | Extraterritorial | 2002 |
| Kajous Tech Limited | Wholesale & retail | 2019 |
| Kalahomes Ltd | Real estate | 2020 |
| Kalamart Services Limited | Professional & scientific | 2003 |
| Kalamart Properties Limited | Real estate | 2001 |
| Kalar Properties Ltd | Real estate | 2020 |
| Kale Learning Limited | Transport & logistics | 2015 |
| KALEEM7644 Ltd | Wholesale & retail | 2025 |
| Kaleidox Ltd | Wholesale & retail | 2026 |
| Kalhan Limited | Wholesale & retail | 1999 |
| Kalico Clothing Limited | Wholesale & retail | 2025 |
| Kallolar Limited | Wholesale & retail | 2024 |
| Kalsons Limited | Wholesale & retail | 1983 |
| KAM Beauty Bar Limited | Other services | 2024 |
| Kamal Limited | Wholesale & retail | 1987 |
| Kamilla Trade Limited | Wholesale & retail | 2026 |
| Kamkee Limited | Manufacturing | 1999 |
| Kang Build Ltd | Construction | 2024 |
| Kanjan Empire Ltd | Wholesale & retail | 2026 |
| Kaoz London Ltd | Wholesale & retail | 2021 |
| Kapray Clothing Limited | Wholesale & retail | 2005 |
| Kaps Experts Consulting Ltd | Information & communication | 2024 |
| Karakorum Investments Limited | Hospitality | 2005 |
| Karma Services (London) Limited | Administrative & support | 2012 |
| Kashif Go Ltd | Wholesale & retail | 2025 |