| Information Power Ltd | Information & communication | 2006 |
| Ingua Partners Ltd | Information & communication | 2025 |
| Inicio Holdings Limited | Administrative & support | 2023 |
| Inonwa Properties Ltd | Construction | 2023 |
| Inovair Limited | Professional & scientific | 2002 |
| Inovax Consulting Ltd | Professional & scientific | 2026 |
| Insights to Innovation Ltd | Professional & scientific | 2018 |
| Inspirera Limited | Construction | 2010 |
| Intech Capital Limited | Extraterritorial | 2012 |
| Intech Int'L UK Ltd | Professional & scientific | 2011 |
| Integral Consultancy Ltd | Professional & scientific | 2025 |
| Integral Development Corporation (Europe) Limited | Information & communication | 1996 |
| Integral Europe Ltd | Information & communication | 2023 |
| Integritix Limited | Information & communication | 2025 |
| Intelligent Online Property Ltd | Real estate | 2021 |
| International Club for Responsible AI USE Ltd | Other services | 2024 |
| International Investor in Developments Ltd | Construction | 2017 |
| International Land and Developments Limited | Real estate | 2003 |
| Intrepid Business Management Limited | Professional & scientific | 2018 |
| INV3NTIVE Football Academy C.I.C. | Arts & recreation | 2019 |
| Invest 24 PLC | Professional & scientific | 2021 |
| Invest 2GETHER Ltd | Real estate | 2022 |
| Invicara UK Limited | Information & communication | 2017 |
| IO Systech Limited | Information & communication | 2004 |
| Iona BKB Ltd | Professional & scientific | 2023 |
| IPN Holding Ltd | Financial services | 2017 |
| Ipswich Care Home Holdings Limited | Financial services | 2025 |
| Ipswich Care Home Limited | Health & social care | 2023 |
| Ipswich Care Limited | Health & social care | 2025 |
| IRG (Old) WWR Limited | Hospitality | 2015 |
| IRN Data Analysis Ltd | Professional & scientific | 2025 |
| Isad Ltd | Transport & logistics | 2017 |
| Isolution Digi Ltd | Wholesale & retail | 2024 |
| Isosceles Finance Limited | Professional & scientific | 1998 |
| Israt Ltd | Health & social care | 2024 |
| Istrate Accounting Limited | Professional & scientific | 2026 |
| IT Valley (London) Ltd | Information & communication | 2015 |
| It-Contracts Finance Limited | Administrative & support | 2004 |
| Itax Consulting UK Limited | Professional & scientific | 2006 |
| ITW Holdings LP | | 2015 |
| Ivory Enterprises Media Solutions Ltd | Professional & scientific | 2024 |
| Ivory Skin Properties Ltd | Real estate | 2023 |
| IWG Consulting Limited Liability Partnership | | 2017 |
| Izoard Limited | Professional & scientific | 2017 |
| J & J Freight Limited | Transport & logistics | 2018 |
| J & J Freight Services Limited | Transport & logistics | 2018 |
| J & P Services (Surrey) Ltd | Manufacturing | 2024 |
| J H G Holdings Limited | Professional & scientific | 2004 |
| J Major Central Heating Services Ltd | Construction | 2020 |
| J&B Compliance Services Ltd | Professional & scientific | 2025 |
| J&P Exotics Limited | Wholesale & retail | 2019 |
| J&S Residentials Limited | Real estate | 2024 |
| J. Gardner Holdings Limited | Construction | 1913 |
| J2F Property Ltd | Real estate | 2019 |
| Jaca Limited | Professional & scientific | 2017 |
| Jacana Interiors Ltd | Professional & scientific | 2017 |
| Jade Real Estate Limited | Real estate | 2021 |
| Jager & Horn Capital Ltd | Real estate | 2026 |
| Jaguar Hairdressing Supplies Ltd | Wholesale & retail | 2018 |
| Jahan Investment Homes Limited | Real estate | 2022 |
| James Knight Group Limited | Wholesale & retail | 2020 |
| Janssen BTL Ltd | Real estate | 2021 |
| Jasmine Tree Limited | Wholesale & retail | 2016 |
| Jaxs Gym Ltd | Arts & recreation | 2024 |
| JBC Investment Management Limited | Real estate | 2005 |
| JC Homes & Property Ltd | Real estate | 2025 |
| Jeas Stiftung Ltd | Other services | 2025 |
| Jessamel Limited | Construction | 2018 |
| Jessica Martin Associates Ltd. | Professional & scientific | 2016 |
| JF Invest Ltd | Real estate | 2023 |
| JG Consulting Works Limited | Administrative & support | 2016 |
| JHB Accountancy Services Ltd | Professional & scientific | 2018 |
| JIL Property Ltd | Real estate | 2026 |
| Jimk Real Estate Ltd | Real estate | 2021 |
| Jingguang Ltd | Professional & scientific | 2025 |
| JJ Accounting Ltd | Professional & scientific | 2023 |
| JKR Jointing Ltd | Construction | 2025 |
| JM Pillar Ltd | Real estate | 2026 |
| JM Security Ltd | Administrative & support | 2019 |
| JMA Property Investments Ltd | Real estate | 2024 |
| JMC Scientific Consulting Limited | Professional & scientific | 2013 |
| JML Management Solutions Limited | Information & communication | 2011 |
| JN UK Participations Ltd | Financial services | 2024 |
| Jnfx Limited | Professional & scientific | 2007 |
| JO Endoro Atelier Ltd | Professional & scientific | 2020 |
| Jobbeke Unlimited Ltd | Real estate | 2025 |
| Joda's Pugs & Dogs Ltd | Other services | 2023 |
| Jogs Real Estate Ltd | Real estate | 2025 |
| Johansson Ltd | Real estate | 2024 |
| John Palmer Senior & Co Ltd | Wholesale & retail | 2016 |
| Johnjames Investments Ltd | Real estate | 2021 |
| Johnson and Johnson Property Ltd | Real estate | 2025 |
| Johnsons Properties Ltd | Real estate | 2017 |
| JOI Capital Ltd | Real estate | 2025 |
| Jois Capital Ltd | Real estate | 2025 |
| Jolo Homes Ltd | Real estate | 2026 |
| Jovan Investments Limited | Financial services | 2016 |
| JP Greenstreet Bricks Properties Ltd | Real estate | 2021 |
| JRR Hotels Ltd | Hospitality | 2021 |
| JSH UK Holdings Ltd | Financial services | 2018 |