| Investigative Minds (IMS) Ltd | Real estate | 2014 |
| Investmentsfx Limited | Financial services | 2024 |
| INZ Holdings Ltd | Real estate | 2025 |
| Ioan Ples Limited | Construction | 2018 |
| Iona Company Limited | Real estate | 1986 |
| Ionel Decorating Ltd | Other services | 2015 |
| IP Delivery Ltd. | Manufacturing | 2018 |
| IPB Property Group Ltd | Real estate | 2021 |
| IPP Xliii Limited | Administrative & support | 2025 |
| IPS Consultancy Services Ltd | Professional & scientific | 2003 |
| IR Electricals & Security Ltd | Construction | 2023 |
| IRB Trading Ltd | Wholesale & retail | 2020 |
| IRM Holdings Ltd | Real estate | 2025 |
| Ironcraft Fabrications Ltd | Manufacturing | 2025 |
| IS London Ltd | Other services | 2021 |
| Island Concierge Limited | Professional & scientific | 2019 |
| Island Fishcy Limited | Hospitality | 2026 |
| Island Gardens Limited | Construction | 2002 |
| Islands Discounts Limited | Wholesale & retail | 2014 |
| Islat Trading Limited | Wholesale & retail | 2025 |
| Islington Auto Services Limited | Wholesale & retail | 2015 |
| ISO London Limited | Other services | 2014 |
| Issku Ltd | Hospitality | 2024 |
| IT Sorcery Ltd | Information & communication | 2012 |
| Ithaca Coaching UK Ltd | Education | 2023 |
| Ithiel Partners Ltd | Professional & scientific | 2020 |
| Itinstock Ltd | Wholesale & retail | 2020 |
| Ivan 80 Ltd | Construction | 2019 |
| Ivovovi Limited | Administrative & support | 2026 |
| IVY22 Ltd | Wholesale & retail | 2025 |
| Iyamah-Kmh-Care Ltd | Health & social care | 2016 |
| J & A-M Real Estates Limited | Real estate | 2020 |
| J & B Services Edmonton Ltd | Other services | 2014 |
| J & B Target Construction Ltd | Construction | 2026 |
| J & LI Real Estates Limited | Real estate | 2020 |
| J & LLG Real Estates Limited | Real estate | 2024 |
| J & T Logistics & Sales UK Ltd | Financial services | 2017 |
| J B Design & Building Limited | Construction | 2026 |
| J Nairne Consulting Ltd | Construction | 2020 |
| J O’Sullivan PUB Consulting Ltd | Professional & scientific | 2025 |
| J T Salon Limited | Other services | 2019 |
| J T Services (Herts) Ltd | Other services | 2020 |
| J Tait Marketing Services Ltd | Professional & scientific | 2023 |
| J&Z Defence Ltd | Public administration | 2022 |
| J. Cooke Engineering Limited | Manufacturing | 1973 |
| J. J. Burling Limited | Construction | 1996 |
| J. R. Nart Limited | Real estate | 2024 |
| J.A.R. Homes Limited | Real estate | 2018 |
| J.A.R.C.E. Services Ltd | Wholesale & retail | 2019 |
| J.B.R Engineering Services Limited | Professional & scientific | 2017 |
| J.C.A.M. Services Ltd | Construction | 2019 |
| J.E.T.A Investments Limited | Real estate | 2022 |
| J.F. Electrical Contractors Limited | Construction | 2008 |
| J26 Trucking Limited | Transport & logistics | 2017 |
| JA Haylock Holdings Limited | Professional & scientific | 2020 |
| JAB Scaffolding Services Ltd | Construction | 2020 |
| Jack Plant Limited | Professional & scientific | 2016 |
| Jacks Wheels Ltd | Transport & logistics | 2025 |
| Jackson U.K. Limited | Construction | 2024 |
| Jacob Holmes Ltd | Professional & scientific | 2025 |
| Jagger Property Limited | Real estate | 2017 |
| JAK Clearance Ltd | Administrative & support | 2020 |
| JAL Buildings Limited | Real estate | 2025 |
| JAL Produce Limited | Wholesale & retail | 2016 |
| Jamaican Dutchpot Kitchen Ltd | Hospitality | 2025 |
| Jamesmead Developments Limited | Construction | 2023 |
| Jameswitt Electrical Ltd | Construction | 2021 |
| Jamjac Foods and Logistics Limited | Hospitality | 2025 |
| Jampetlink Health Care Services UK Ltd | Health & social care | 2023 |
| Janes Plants Ltd | Wholesale & retail | 2025 |
| Jasco Productions Ltd | Information & communication | 2017 |
| Jase Foods Ltd | Hospitality | 2022 |
| Jasecoop Ltd | Wholesale & retail | 2012 |
| JAX PR Limited | Professional & scientific | 2019 |
| Jaxon James Developments Limited | Construction | 2017 |
| Jaydenvn Properties Ltd | Real estate | 2025 |
| JBC Automotive Ltd | Wholesale & retail | 2025 |
| JBS Holdings Ltd | Real estate | 2019 |
| JBS Plumbing and Heating Ltd | Construction | 2017 |
| JBV London Ltd | Hospitality | 2023 |
| JC Group Property Services Ltd | Construction | 2025 |
| JCA Autos Ltd | Wholesale & retail | 2022 |
| JCA Education Ltd | Education | 2022 |
| JCC Capital Limited | Financial services | 2025 |
| JD Power Properties Ltd | Real estate | 2024 |
| JDL Portfolios Limited | Real estate | 2021 |
| JDL Property Management Ltd | Construction | 2017 |
| Jeico 3 Limited | Real estate | 2012 |
| Jelleystone Limited | Information & communication | 2025 |
| Jengaz Safety First Ltd | Wholesale & retail | 2025 |
| JEP London Ltd | Real estate | 2021 |
| Jerex Holdings Ltd | Real estate | 2024 |
| Jerex Ltd | Real estate | 2024 |
| JEV Care Limited | Health & social care | 2022 |
| Jewish Joint Burial Society | Other services | 1968 |
| JG Flow and Return Ltd | Construction | 2025 |
| JH Clarity Limited | Administrative & support | 2024 |
| Jiggins and Sons Limited | Extraterritorial | 2012 |
| JIL Homes Ltd | Health & social care | 2020 |
| Jinling Quad Parts Ltd | Wholesale & retail | 2019 |