| Islamic WAL ART1 Limited | Arts & recreation | 2025 |
| Island Flavours Ltd | Hospitality | 2009 |
| Island Soul Cuisine Ltd | Hospitality | 2019 |
| Isle of Law Ltd | Professional & scientific | 2022 |
| Ismart Consultancy Limited | Real estate | 2014 |
| Isradrive Ltd | Transport & logistics | 2025 |
| Istelia Limited | Transport & logistics | 2026 |
| IT Solution Experts Ltd | Wholesale & retail | 2023 |
| Italian Bangladeshi UK Organisation Limited | Other services | 2018 |
| Itauk Limited | Wholesale & retail | 2026 |
| ITECH3 Ltd | Wholesale & retail | 2023 |
| Itek Electrical Ltd | Construction | 2021 |
| ITH EYE Ltd | Professional & scientific | 2025 |
| ITL Global Recruitment UK Ltd | Administrative & support | 2022 |
| Iustin Marian Limited | Construction | 2023 |
| IVANOS85 Limited | Wholesale & retail | 2025 |
| Ivanushki Limited | Transport & logistics | 2016 |
| Ivben Services Limited | Administrative & support | 2025 |
| IVC Electrical Limited | Construction | 2015 |
| IVY Global Ltd | Wholesale & retail | 2019 |
| IWA Green Consulting Limited | Other services | 2022 |
| IY Traders Ltd | Construction | 2024 |
| IZ Energy Services Ltd | Construction | 2013 |
| Izcon Technology Limited | Information & communication | 2014 |
| Izdani Properties Limited | Real estate | 2023 |
| Izzu Ltd | Wholesale & retail | 2024 |
| J & J Unique Services Limited | Construction | 2022 |
| J & M Ventures Ltd | Wholesale & retail | 2016 |
| J & P Mortgages Ltd | Financial services | 2021 |
| J & S Star Property Ltd | Real estate | 2016 |
| J Heating & Plumbing Ltd | Construction | 2016 |
| J N Jacobs Limited | Professional & scientific | 2019 |
| J S Logistics & Recovery Ltd | Transport & logistics | 2022 |
| J VIO Limited | Transport & logistics | 2019 |
| J&A Courier Services Ltd | Transport & logistics | 2023 |
| J&I Solutions Ltd | Extraterritorial | 2025 |
| J&K Properties London Ltd | Real estate | 2024 |
| J&S Security (London) Ltd | Administrative & support | 2013 |
| J&S Services 247 Ltd | Administrative & support | 2015 |
| J'S Calculated & Co Ltd | Manufacturing | 2024 |
| J.A. Phillips Associates Limited | Construction | 1995 |
| J.A. Phillips Consultancy LLP | | 2007 |
| J.A. Phillips Holdings Limited | Professional & scientific | 1991 |
| J.R. Capital Group Ltd | Education | 2019 |
| J.W. Grant (UK) Co. Ltd | Manufacturing | 2009 |
| JA Heatcare Ltd | Professional & scientific | 2015 |
| Jabez Works Ltd | Wholesale & retail | 2022 |
| JAC Metal Works Limited | Manufacturing | 2008 |
| JAC Property Solutions Limited | Real estate | 2013 |
| Jack Leon Ltd | Transport & logistics | 2015 |
| Jack Online Trading Ltd | Wholesale & retail | 2020 |
| Jack's Education Limited | Education | 2025 |
| Jacobs Apps Ltd | Information & communication | 2025 |
| Jada Moto Ltd | Wholesale & retail | 2019 |
| Jaffna Foods Ltd | Wholesale & retail | 2022 |
| Jaha Solutions Limited | Administrative & support | 2017 |
| Jahan's Empire Ltd | Real estate | 2024 |
| Jahzara Future Services Limited | Health & social care | 2024 |
| JAI Bhole Ltd | Wholesale & retail | 2022 |
| Jaisol Ltd | Hospitality | 2025 |
| Jaklite Limited | Financial services | 2011 |
| Jamaal Pharm Ltd | Health & social care | 2024 |
| Jamaibou Limited | Transport & logistics | 2022 |
| Jamali & Sons Ltd | Real estate | 2024 |
| Jamen LLP | | 2014 |
| James 1 Properties Ltd | Real estate | 2023 |
| James Leigh Limited | Wholesale & retail | 1946 |
| Jamia Almaarif | Health & social care | 2018 |
| Jana Hock Ltd | Information & communication | 2025 |
| Janat Shira Ltd | Health & social care | 2021 |
| Jannat Accessories Ltd | Wholesale & retail | 2024 |
| Jannath Dina Ltd | Hospitality | 2020 |
| Jannathul Ummah Academy Ltd | Health & social care | 2025 |
| Janor Ltd | Construction | 2018 |
| Japabudz Ltd | Information & communication | 2025 |
| Japanese Bishop Limited | Hospitality | 2026 |
| Japanese Bowl Limited | Hospitality | 2026 |
| Japanese Hackney Limited | Hospitality | 2026 |
| Jarek DUK Media Ltd | Professional & scientific | 2024 |
| Jasannorganics Limited | Manufacturing | 2019 |
| Jasco Construction Ltd | Construction | 2022 |
| Jaseeth Care Services Limited | Administrative & support | 2025 |
| Jasmac Productions Limited | Professional & scientific | 2021 |
| Jasmine Ysobel Ltd | Health & social care | 2025 |
| Jass Home Improvements Limited | Real estate | 2017 |
| Javid & Co. Limited | Hospitality | 2026 |
| JAY & JON Ltd | Wholesale & retail | 2023 |
| JAY Auto Servicing Ltd | Wholesale & retail | 2025 |
| JAY Catering Supplies Limited | Wholesale & retail | 2025 |
| JAY Kadn Music Ltd | Information & communication | 2025 |
| Jay-Kay Hub Ltd | Wholesale & retail | 2024 |
| Jaybright Media Ltd. | Transport & logistics | 2016 |
| Jayp Roofing Limited | Construction | 2014 |
| Jaystarr Security Limited | Extraterritorial | 2015 |
| JB Portfolio Ltd | Real estate | 2023 |
| Jbdn Ltd | Information & communication | 2025 |
| JBF Management & Consultant Limited | Construction | 2016 |
| Jbms Maintenance Services Ltd | Construction | 2019 |
| JBO Property Limited | Real estate | 2019 |
| Jbrr Investments Limited | Other services | 2024 |