| Ironstone Trading Group Ltd | Water & waste | 2026 |
| IS Jointing Ltd | Construction | 2023 |
| ISK Holdings Ltd | Real estate | 2024 |
| Isom Electrical Ltd | Construction | 2011 |
| Isten Hozott Ltd | Wholesale & retail | 2024 |
| IT Accounts Ltd | Professional & scientific | 2024 |
| It's a Funny Life Films Ltd | Information & communication | 2017 |
| It's Marketing Limited | Financial services | 2012 |
| It's Your Beauty Ltd | Other services | 2018 |
| It-Remedy Ltd | Extraterritorial | 2014 |
| Itcompete Limited | Information & communication | 2019 |
| Ithought Solutions Limited | Information & communication | 2014 |
| Itnoa Services Limited | Health & social care | 2021 |
| Itrosa Limited | Professional & scientific | 2009 |
| ITS Bioscience Ltd | Professional & scientific | 2025 |
| Itsjustmine Ltd | Wholesale & retail | 2020 |
| IV Boost UK Limited | Health & social care | 2014 |
| Ivasco Groundworker Ltd | Construction | 2019 |
| IVY and Abel Properties Ltd | Real estate | 2024 |
| IVY Rose London Ltd | Other services | 2019 |
| Ivy-Ana & Co Ltd | Other services | 2017 |
| Ixpand Software Solutions Ltd | Information & communication | 2021 |
| J & J Communications Ltd | Information & communication | 2011 |
| J & J Land and Property Ltd | Real estate | 2025 |
| J & J Tyres Limited | Wholesale & retail | 2009 |
| J & M Associates Ltd | Real estate | 2018 |
| J & P Properties (London) Limited | Real estate | 2014 |
| J & T Construction Design Ltd | Construction | 2018 |
| J a Associates (UK) Limited | Professional & scientific | 2007 |
| J Allsopp & Sons Limited | Construction | 2017 |
| J Apex Property Solutions Ltd | Real estate | 2026 |
| J B Consulting Specialist Limited | Information & communication | 2024 |
| J C Meats Limited | Wholesale & retail | 2013 |
| J C Property Lettings Ltd | Real estate | 2022 |
| J Godson Limited | Health & social care | 2013 |
| J Hallier Electrical Ltd | Construction | 2025 |
| J Hare Research Limited | Professional & scientific | 2024 |
| J Ibello Limited | Professional & scientific | 2009 |
| J J Building Contractors Ltd | Construction | 2020 |
| J J Cleaning Services Limited | Other services | 2001 |
| J Lancaster Ltd | Construction | 2024 |
| J N Home Improvements & Construction Ltd | Construction | 2020 |
| J Nelson Properties Ltd | Real estate | 2023 |
| J P & L Exotics Ltd | Wholesale & retail | 2008 |
| J R Goss Properties Limited | Real estate | 2019 |
| J Rail Management Limited | Professional & scientific | 2023 |
| J Rich Limited | Hospitality | 2022 |
| J Sport Management Limited | Professional & scientific | 2023 |
| J Uddin Locum Limited | Health & social care | 2016 |
| J Ward Construction Ltd | Construction | 2024 |
| J Z Windows Ltd | Construction | 2017 |
| J&E Gill Ltd | Real estate | 2026 |
| J&G Spotless Limited | Other services | 2017 |
| J&H Auto Repairs Ltd | Wholesale & retail | 2018 |
| J&S Clean Solutions Ltd | Administrative & support | 2025 |
| J&T Estates Ltd | Real estate | 2026 |
| J. E. M. Flow Limited | Administrative & support | 2010 |
| J.A Plumbing and GAS Services Ltd | Construction | 2022 |
| J.C. Appleby Associates Ltd | Administrative & support | 2014 |
| J.D. Personnel Limited | Construction | 1999 |
| J.D. Properties (UK) Limited | Construction | 2009 |
| J.J.B. Electrical & Services Limited | Construction | 2005 |
| J.S Opal Consulting Limited | Professional & scientific | 2014 |
| J.W. Builders & Developers Limited | Construction | 2005 |
| J.Zanelli Limited | Administrative & support | 2025 |
| J2K Bespoke Interiors Ltd | Construction | 2022 |
| JA Videography Ltd | Manufacturing | 2023 |
| Jaaz Limited | Health & social care | 2008 |
| JAB Maude Ltd | Information & communication | 2025 |
| Jacaulfield Limited | Administrative & support | 2016 |
| Jack and Jill Kids PTY Limited | Wholesale & retail | 2011 |
| Jack and Jill's Preschool Limited | Education | 2017 |
| Jackson Coldroom Services Limited | Manufacturing | 2015 |
| Jackson DEL Fuego Limited | Information & communication | 2018 |
| Jackson Smith Limited | Information & communication | 2016 |
| Jacobs Ducting and Plumbing Ltd | Construction | 2024 |
| Jadosh Project Limited | Construction | 2016 |
| Jagl Properties Limited | Real estate | 2024 |
| JAI HO Sankar Ltd | Construction | 2024 |
| Jaira Solutions Ltd | Education | 2022 |
| James a Robertson and Associates Limited | Professional & scientific | 2013 |
| James Bradley Mechanical Ltd | Construction | 2024 |
| James Grace Construction Ltd | Construction | 2007 |
| James Miller and Associates Limited | Information & communication | 1995 |
| James Newman Solutions Limited | Administrative & support | 2014 |
| James Tinsley Limited | Information & communication | 2010 |
| Jammybeggar Limited | Real estate | 2018 |
| Janala UK Ltd | Health & social care | 2022 |
| Janejok Care Services Limited | Transport & logistics | 2023 |
| Janes Jungle Ltd | Wholesale & retail | 2023 |
| Janvi Ltd | Health & social care | 2017 |
| Jaques Solutions Ltd | Construction | 2008 |
| Jasl Limited | Professional & scientific | 2022 |
| Jaslyn and Sarjan Property Management Limited | Real estate | 2026 |
| Jasmin Estates Limited | Real estate | 2015 |
| Jaspa (U K) Limited | Hospitality | 1977 |
| Jaspa Investments Limited | Real estate | 2004 |
| Jasroj Facilities Limited | Hospitality | 2025 |
| Jayde Properties Limited | Real estate | 2022 |
| Jayden Thompson Limited | Real estate | 2025 |