| Itso Tech Limited | Construction | 2008 |
| Ittd Ltd | Information & communication | 2024 |
| Ittm (UK) Ltd | Professional & scientific | 2020 |
| Iubentium Ltd | Wholesale & retail | 2021 |
| IV Cleaning & Transport Services Ltd | Administrative & support | 2019 |
| Ivan Dolac Property (UK) Limited | Real estate | 2004 |
| Ivaos Limited | Professional & scientific | 2014 |
| Ivie Omenai Limited | Construction | 2011 |
| IVO and the BEA Ltd | Information & communication | 2026 |
| Ivory Place Limited | Households | 2009 |
| IZ Consultancy Limited | Financial services | 2018 |
| IZH Holdings Ltd | Professional & scientific | 2015 |
| Izidio Carpet Cleaning Ltd | Administrative & support | 2024 |
| Iziproperty Ltd | Real estate | 2025 |
| J & a Prestigiacomo Catering Ltd | Hospitality | 2015 |
| J LEE Homes Ltd | Construction | 2022 |
| J M Transport (Hitchin) Ltd | Transport & logistics | 2011 |
| J Mansolas Consultants Ltd | Professional & scientific | 2022 |
| J Pitt Consulting Limited | Information & communication | 2017 |
| J Roberts Roofing Limited | Construction | 2024 |
| J Samuel Limited | Health & social care | 2015 |
| J Tanna & Co Limited | Professional & scientific | 2015 |
| J&K Agricultural Services Limited | Wholesale & retail | 2022 |
| J. R. Holmes & Co Ltd | Professional & scientific | 2012 |
| J.J Tailoring Ltd | Manufacturing | 2023 |
| J.K. Grass Roots Foundation Limited | Health & social care | 2014 |
| J.W. Munroe Construction (UK) Limited | Construction | 2001 |
| J4 Media Limited | Information & communication | 2009 |
| JA Living Solutions Ltd | Real estate | 2025 |
| JA Stoneworld Ltd | Wholesale & retail | 2025 |
| Ja.Management Ltd | Professional & scientific | 2025 |
| Jacaranda Meadow Bespoke Complex Care Ltd | Health & social care | 2026 |
| Jack's Wardrobes Ltd | Wholesale & retail | 2025 |
| Jackson Computing Limited | Information & communication | 2024 |
| Jackson Sculpture Conservation Ltd | Other services | 2010 |
| Jacquemus LE Royaume-Uni Limited | Wholesale & retail | 2023 |
| Jade Mendes Aesthetics Ltd | Other services | 2019 |
| JAF Construction Ltd | Real estate | 2010 |
| Jafri Properties Ltd | Real estate | 2021 |
| James Lambourne Properties Limited | Administrative & support | 2008 |
| James Stratten Financial Planning Limited | Financial services | 2008 |
| James Wright Building Limited | Construction | 2021 |
| Jamie Stoddart Ltd | Professional & scientific | 2026 |
| Jamie Viljoen Consulting Limited | Professional & scientific | 2024 |
| JAN Property Limited | Real estate | 2016 |
| Jane Goddard Consultancy Services Ltd | Professional & scientific | 2025 |
| Jane Ward Holistic Health Ltd | Other services | 2023 |
| Janet Simpkins Limited | Professional & scientific | 2002 |
| JAR Ahead Limited | Real estate | 2022 |
| Jardine Capital Limited | Professional & scientific | 2011 |
| Jardine Capital Property Limited | Real estate | 2025 |
| Jasmin Services Limited | Financial services | 2016 |
| Jasmine Alice Limited | Other services | 2024 |
| Jason Bros Property Ltd | Construction | 2024 |
| Jatida Limited | Real estate | 2020 |
| JAY One Fulfilment Ltd | Wholesale & retail | 2023 |
| JAY Ramji Ltd | Wholesale & retail | 2023 |
| Jayne Coates Counselling Ltd | Health & social care | 2023 |
| Jayousi Limited | Professional & scientific | 2020 |
| JB Travel Solutions Limited | Administrative & support | 2014 |
| JB29 Marketing Services Ltd | Professional & scientific | 2022 |
| JBT Music Ltd | Information & communication | 2025 |
| JC Lofts Limited | Construction | 2019 |
| JC Prime Group Ltd | Real estate | 2023 |
| Jectus Properties Ltd. | Real estate | 2000 |
| JEF Legal Limited | Professional & scientific | 2023 |
| JEM Marketing & Fulfilment Services Ltd | Administrative & support | 2009 |
| Jemmett Park Architecture Ltd | Professional & scientific | 2025 |
| JEN Kavanagh Ltd | Arts & recreation | 2022 |
| Jenkins Emporium Ltd | Manufacturing | 2024 |
| Jenna Nails Ltd | Other services | 2025 |
| Jess-Cooke Limited | Arts & recreation | 2011 |
| Jess-Cooke Services Limited | Administrative & support | 2025 |
| Jessco (Management Services) Limited | Other services | 1974 |
| JET Whales Limited | Administrative & support | 2012 |
| Jeyam (PVT) Limited | Wholesale & retail | 2015 |
| JF Construction & Developments Ltd | Real estate | 2024 |
| JF Plumbing & Heating Specialists Ltd | Construction | 2024 |
| JFL Trading Limited | Households | 2025 |
| JFW Medical Limited | Health & social care | 2017 |
| JG Core Group Limited | Financial services | 2024 |
| JH365 Ltd | Construction | 2026 |
| JHG Health Limited | Health & social care | 2023 |
| JHI Studio Limited | Information & communication | 2022 |
| JI Chicken Properties Ltd | Real estate | 2024 |
| JI Kingston Ltd | Hospitality | 2023 |
| JI Lewisham Ltd | Hospitality | 2023 |
| JIB OP Television Ltd | Information & communication | 2011 |
| JIB Properties Limited | Real estate | 2016 |
| JIN H Property Ltd | Real estate | 2016 |
| Jinzhen Health Care Ltd | Public administration | 2026 |
| Jiurong UK Ltd | Professional & scientific | 2016 |
| Jive (UK) Limited | Wholesale & retail | 2004 |
| JJ Bros Construction Ltd | Construction | 2025 |
| JJ Chauffeurs Ltd | Transport & logistics | 2022 |
| Jjlove Productions Limited | Information & communication | 2023 |
| Jjrt Developments Ltd | Construction | 2020 |
| JK Compliance Consultancy Ltd | Professional & scientific | 2019 |
| JK Moon Property Ltd | Construction | 2024 |
| JKT Ventures Limited | Real estate | 2024 |