| IT Zero Ltd | Information & communication | 2016 |
| Italian Finests Ltd | Wholesale & retail | 2022 |
| ITC Property Service Limited | Real estate | 2023 |
| ITC Training Limited | Education | 2024 |
| Itdir Ltd | Transport & logistics | 2025 |
| Ithoreca Ltd | Information & communication | 2025 |
| Itnets Limited | Information & communication | 2024 |
| ITP - International Travel Partnership Limited | Information & communication | 1986 |
| Itve Ltd | Professional & scientific | 2018 |
| Ivan Sopher LLP | | 2014 |
| IVAN88 Ltd | Construction | 2017 |
| Ivoryvale Limited | Wholesale & retail | 1998 |
| IVY Road Productions Ltd | Information & communication | 2025 |
| Iwoo Limited | Information & communication | 2014 |
| Izbuc Trans Ltd. | Transport & logistics | 2025 |
| J & a Wells Ltd | Information & communication | 2016 |
| J & J Property Management Limited | Other services | 2012 |
| J & K Finance Consultancy Limited | Professional & scientific | 2019 |
| J & K Projects Limited | Construction | 2022 |
| J & L Carpentry Limited | Construction | 2010 |
| J & T London Limited | Health & social care | 2016 |
| J C Stage Solutions Limited | Arts & recreation | 2024 |
| J D Synergy Ltd | Real estate | 2017 |
| J E L Solutions Limited | Financial services | 2002 |
| J Egner Art Ltd | Arts & recreation | 2017 |
| J Franks Interiors Limited | Wholesale & retail | 2021 |
| J Gill Transport Ltd | Transport & logistics | 2016 |
| J Hill Ltd | Wholesale & retail | 2023 |
| J I F Group Limited | Construction | 2015 |
| J JAY Motors Ltd | Wholesale & retail | 2021 |
| J M Harji Construction Limited | Construction | 2016 |
| J P M Capital Finance Limited | Financial services | 2015 |
| J&A Haulage Solutions Ltd | Transport & logistics | 2026 |
| J&J Holding Ltd | Construction | 2015 |
| J&P Thomas Developments Limited | Construction | 2003 |
| J&Sw Properties Ltd | Real estate | 2017 |
| J-Kinetic Ltd | Arts & recreation | 2026 |
| J. B. Tatam Luxury Gifts Ltd | Other services | 1961 |
| J. Kariuki Ltd | Information & communication | 2026 |
| J. Reddington Ltd | Construction | 1996 |
| J.A Travel Ltd | Transport & logistics | 2026 |
| J.Cox Props Ltd | Professional & scientific | 2022 |
| J.S.L. Developments Limited | Real estate | 1959 |
| J1L1 Limited | Real estate | 2026 |
| JA Rigging Ltd | Construction | 2022 |
| Jabber Media Limited | Administrative & support | 2007 |
| Jacana People Ltd | Arts & recreation | 2025 |
| Jace Transportation LLP | | 2015 |
| Jack Burrito Limited | Hospitality | 2017 |
| Jack Powell Props Ltd | Information & communication | 2024 |
| Jackson Film & TV Limited | Arts & recreation | 2021 |
| Jackw Stag Ltd | Construction | 2025 |
| Jacmen(Investments)Limited | Real estate | 1964 |
| Jacobs & Co Motorsports Limited | Wholesale & retail | 2026 |
| Jacqueline Hurst Therapy Ltd | Other services | 2013 |
| Jadawn Properties Ltd | Real estate | 2018 |
| Jadawn Property Holdings Limited | Real estate | 2019 |
| Jadebricks (Charles Street) Ltd | Construction | 2023 |
| Jadebricks London Ltd | Construction | 2020 |
| Jadebricks Manchester Ltd | Construction | 2020 |
| Jaded London Limited | Wholesale & retail | 2008 |
| Jafari Services Limited | Administrative & support | 2014 |
| Jaffalight Limited | Administrative & support | 1983 |
| JAG Wholesale Ltd | Wholesale & retail | 2013 |
| Jagmama Brothers Limited | Wholesale & retail | 2025 |
| Jaikrithin Technologies Limited | Information & communication | 2014 |
| Jaiswal Investment Group Limited | Real estate | 2017 |
| JAJ BIZ Ltd | Financial services | 2026 |
| Jakar International Limited | Wholesale & retail | 1951 |
| Jakd Medical Services Limited | Professional & scientific | 2025 |
| Jakubs TM Ltd | Transport & logistics | 2025 |
| Jala Beverages Limited | Hospitality | 2020 |
| JAM One Property Limited | Real estate | 2022 |
| JAM Roll Rigging Logistics Ltd | Professional & scientific | 2018 |
| Jambcalm Ltd | Professional & scientific | 2025 |
| James Berlin & Associates Limited | Other services | 2012 |
| James Hulme Holdings Limited | Hospitality | 2019 |
| James Steel Limited | Manufacturing | 2011 |
| Jamie Knight Carpentry & Joinery Ltd | Construction | 2015 |
| Jamie Stevens (Kensington) Ltd | Other services | 2012 |
| Jamiejo Ltd | Wholesale & retail | 2025 |
| Jams Properties Ltd | Real estate | 2015 |
| Jamsam Consulting Ltd | Professional & scientific | 2022 |
| Jamtal Limited | Administrative & support | 2019 |
| Jamuna Restaurant London Ltd | Hospitality | 2017 |
| Jamz Digital Ltd | Information & communication | 2020 |
| Janani Bodhi Ltd | Health & social care | 2023 |
| Janemanu Limited | Health & social care | 2019 |
| Janemore Services Ltd. | Transport & logistics | 2011 |
| Jani Trading Company Limited | Wholesale & retail | 1973 |
| Janklow & Nesbit (UK) Limited | Administrative & support | 2000 |
| Janmed Limited | Health & social care | 2016 |
| Janus Assets Ltd | Extraterritorial | 2021 |
| Jaolel Pescqui Limited | Real estate | 2023 |
| JAR TV Limited | Information & communication | 2008 |
| Jarawa Home Services Ltd | Construction | 2025 |
| JAS (Innovations) Limited | Financial services | 2011 |
| JAS Prime Transport Ltd | Transport & logistics | 2026 |
| Jaslyn Properties Ltd | Real estate | 2022 |
| Jason Bamforth Ltd | Information & communication | 2016 |