| Islandbridge Property Holdings Limited | Professional & scientific | 2023 |
| Isle of Dogs Developments 2 Limited | Construction | 2013 |
| Isle of Dogs Developments Limited | Construction | 2013 |
| Isopod Holdings Limited | Financial services | 1997 |
| Ist-Lon Limited | Financial services | 2022 |
| IT Staff Ltd | Administrative & support | 2016 |
| It's a Feeling Ltd | Arts & recreation | 2025 |
| Itdp Solutions Limited | Information & communication | 2004 |
| Itsp Limited | Information & communication | 2022 |
| Ivenco Builders Ltd | Construction | 2013 |
| IVK - Carpet, Upholstery & Hard Floor Cleaning Ltd | Other services | 2025 |
| IVM Building Services Ltd | Construction | 2013 |
| Izel Local Ltd | Wholesale & retail | 2019 |
| IZF Management Ltd | Professional & scientific | 2012 |
| J & a Sahota Limited | Real estate | 2024 |
| J & J Exports UK Ltd | Wholesale & retail | 2021 |
| J & P Fosh LLP | | 2023 |
| J & R Psychology Ltd | Health & social care | 2021 |
| J & T Leasing Limited | Real estate | 2013 |
| J Bond 18 Limited | Professional & scientific | 2025 |
| J Campos Ltd | Construction | 2014 |
| J Cleaner Service Ltd | Administrative & support | 2021 |
| J Day Services Ltd | Other services | 2020 |
| J Florence Ltd | Wholesale & retail | 2020 |
| J Group Asset Management Limited | Real estate | 2026 |
| J Group Construct Ltd | Construction | 2011 |
| J Group Holdings Limited | Professional & scientific | 2012 |
| J Group Smallfield Limited | Construction | 2026 |
| J Group SPV23 Limited | Construction | 2026 |
| J Homeland Ltd | Real estate | 2023 |
| J K Surveys Limited | Professional & scientific | 2015 |
| J M Rail Services Ltd | Construction | 2019 |
| J MOI & Company Limited | Professional & scientific | 2002 |
| J P Aero Holdings Limited | Financial services | 2026 |
| J P Aero Investments Limited | Financial services | 2026 |
| J Rowland Property Ltd | Real estate | 2019 |
| J S Gill Properties Limited | Real estate | 2016 |
| J Stein Properties Ltd | Real estate | 2025 |
| J&M Fragrance House Ltd | Wholesale & retail | 2026 |
| J. Blowes Construction Limited | Construction | 2005 |
| J. L. Reinforcements Ltd | Construction | 2006 |
| J. Ottaway Ltd | Wholesale & retail | 2021 |
| J. Reid Piano Hire Limited | Administrative & support | 1986 |
| J.A.M. Chestnut Management Limited | Financial services | 2016 |
| J.A.M. Contracts Ltd | Information & communication | 2013 |
| J.D.M Mechanical Limited | Construction | 2021 |
| JAC & Drill Consulting Limited | Professional & scientific | 2016 |
| Jacco Macacco Films Ltd | Administrative & support | 2024 |
| Jack Luckhurst Ltd | Other services | 2024 |
| Jack Merrifield Limited | Other services | 2017 |
| Jack Pierce (London) Limited | Arts & recreation | 2010 |
| Jackie Millman Consultancy Ltd | Professional & scientific | 2014 |
| Jackson & Jackson Accountants Limited | Professional & scientific | 1998 |
| Jackson Cohen Associates Ltd | Professional & scientific | 2004 |
| JAD Empire Limited | Information & communication | 2012 |
| Jagannath Hall Alumni Association UK Ltd | Health & social care | 2013 |
| Jagdev Holdings Limited | Financial services | 2026 |
| Jagsport Limited | Administrative & support | 2008 |
| Jahanara Estates Ltd | Real estate | 2025 |
| Jahlivity Limited | Wholesale & retail | 2021 |
| Jahnvi Limited | Wholesale & retail | 2020 |
| JAK Performing Arts Ltd | Arts & recreation | 2016 |
| Jake Omer Ltd | Extraterritorial | 2024 |
| Jakson Repairs Ltd | Other services | 2020 |
| JAL Contract Services Ltd | Construction | 2025 |
| Jalpri Investments Limited | Real estate | 2017 |
| James Argent Limited | Arts & recreation | 2010 |
| James Henry Properties Ltd | Real estate | 2018 |
| James&Swan Limited | Real estate | 2021 |
| Jami Clothing Co. Limited | Other services | 2012 |
| Jamins Kitchen Ltd | Hospitality | 2024 |
| Jandaton Developments Ltd | Real estate | 2015 |
| Jarbs Investments Limited | Real estate | 2013 |
| Jargon Services Limited | Information & communication | 2002 |
| Jarlson & Co Ltd | Wholesale & retail | 2025 |
| Jarm Investments Limited | Real estate | 2024 |
| Jashvim Properties Ltd | Real estate | 2017 |
| Jasmin Properties (UK) Ltd. | Real estate | 2014 |
| Jasmine Food Trading Ltd | Hospitality | 2025 |
| Jasmine Takeaway Ltd | Hospitality | 2022 |
| Jasminealicehome Ltd | Wholesale & retail | 2023 |
| JAX Folly Limited | Construction | 2026 |
| JAY a Bell Ltd | Construction | 2025 |
| Jay's Removal & Courier Solutions Ltd | Transport & logistics | 2022 |
| Jayabbi Real Estate Ltd | Real estate | 2025 |
| Jaymart Rubber & Plastics Limited | Wholesale & retail | 1967 |
| Jayne Wallace Limited | Administrative & support | 2010 |
| JB Corporation Limited | Real estate | 2022 |
| JBB London Limited | Administrative & support | 2013 |
| JBH Groundwork Ltd | Construction | 2021 |
| JBM (IP) Ltd | Information & communication | 2023 |
| JBM Internet Services LLP | | 2012 |
| Jbmk Ltd | Real estate | 2024 |
| JC Group Services Ltd | Construction | 2014 |
| Jcos Group Limited | Financial services | 2021 |
| Jcos Property Investments Limited | Extraterritorial | 2021 |
| Jcps London Ltd | Construction | 2025 |
| JD 99 Limited | Administrative & support | 2007 |
| JD Ducts Limited | Construction | 2021 |
| JD Real Homes Ltd | Real estate | 2021 |