| Idemia UK Pension Trustee Limited | Extraterritorial | 2000 |
| IDL Consulting Ltd | Information & communication | 2022 |
| Ihop Consultancy Ltd | Information & communication | 2026 |
| Imec Consulting Limited | Information & communication | 2008 |
| Imex Data Communications Limited | Information & communication | 1990 |
| Impel Marketing & Digital Limited | Professional & scientific | 2022 |
| Imperial Building Solutions (BD) Ltd | Extraterritorial | 2017 |
| IN Partnership Limited | Financial services | 2013 |
| IN the Park Services Ltd | Administrative & support | 2017 |
| Inductoheat (Tewkesbury) Ltd | Manufacturing | 2004 |
| Inferno Brewery Limited | Manufacturing | 2018 |
| INFIN8 Grafix Ltd | Other services | 2023 |
| INFIN8DESIGNANDPRINT Ltd | Professional & scientific | 2021 |
| Infinity Flooring & Building Ltd | Construction | 2016 |
| Infracare (Midlands) Limited | Professional & scientific | 2003 |
| Infracare (South West) Limited | Professional & scientific | 2002 |
| Infracare Bristol Limited | Professional & scientific | 2003 |
| Infracare Dudley Limited | Professional & scientific | 2005 |
| Infracare East London Limited | Real estate | 2002 |
| Infracare London PS Limited | Construction | 2013 |
| Infracare North West London Limited | Real estate | 2004 |
| Infracare Oxford Limited | Professional & scientific | 2003 |
| Infracare South East London Limited | Real estate | 2004 |
| Infracare Wolverhampton and Walsall Limited | Real estate | 2003 |
| Ingin Limited | Health & social care | 2011 |
| Ingrid West Machinery Limited | Manufacturing | 1968 |
| Initia GC Ltd | Arts & recreation | 2025 |
| Injet Ltd | Professional & scientific | 2023 |
| Innervation Trading Company Limited | Wholesale & retail | 2005 |
| Innervation Trust Limited | Arts & recreation | 2008 |
| Innhurst Consulting Ltd | Information & communication | 2025 |
| Intamarque Group Limited | Financial services | 2019 |
| Intamarque Limited | Wholesale & retail | 2006 |
| Integrated Accommodation Services PLC | Construction | 1999 |
| International Association of Hydrogeologists | Other services | 2000 |
| Intrawise Ltd | Information & communication | 2026 |
| Invictus Elite Ltd | Other services | 2025 |
| Invictus Models Ltd | Other services | 2022 |
| IP Healthcare Ltd | Health & social care | 2022 |
| IPM Trans Logistics Ltd | Transport & logistics | 2017 |
| Ipumps Ltd | Professional & scientific | 2009 |
| Isabella Vrana Limited | Wholesale & retail | 2019 |
| Isis Property Investments Ltd | Real estate | 2008 |
| IT Consultancy Services & Solutions Ltd | Information & communication | 2023 |
| J & J Irwin Lettings Ltd | Real estate | 2018 |
| J & J Scaffolding Contractors Limited | Construction | 2002 |
| J & M Remedial Services Ltd | Administrative & support | 2012 |
| J & R Shearing Limited | Other services | 2010 |
| J & S Property Portfolio Ltd | Real estate | 2022 |
| J Adams Design Limited | Information & communication | 2025 |
| J ASH Padel Ltd | Arts & recreation | 2026 |
| J Bond Civils and Landscaping Ltd | Administrative & support | 2025 |
| J D Autoservice Limited | Wholesale & retail | 2003 |
| J L P Services Limited | Professional & scientific | 1998 |
| J. B. Toolgrinders Limited | Manufacturing | 1994 |
| J.E.M Project Consulting Ltd | Professional & scientific | 2023 |
| J.W. Young & Sons (Fishing Reels) Ltd | Extraterritorial | 2001 |
| J.W. Young & Sons Ltd | Manufacturing | 2001 |
| J.Y.M Autos Ltd | Wholesale & retail | 2017 |
| J4D Limited | Information & communication | 2025 |
| Jack Boskett Media Ltd | Professional & scientific | 2016 |
| Jackie Ventom Training and Consultancy Limited | Education | 2000 |
| Jacks Dive Chest UK Ltd | Education | 2025 |
| JAE Estates Ltd | Real estate | 2020 |
| James Brown Audit and Management Ltd | Professional & scientific | 2022 |
| James Grassick Racing Limited | Arts & recreation | 2014 |
| Jamie Cattermole Limited | Other services | 2017 |
| Jams Property Leasing Ltd | Real estate | 2025 |
| JAN Burrell Art Ltd | Wholesale & retail | 2020 |
| JB Construction (2025) Ltd | Construction | 2025 |
| JBS Construction Group Ltd | Construction | 2025 |
| JBS Construction Holdings Ltd | Other services | 2025 |
| JBS Engineering Services Limited | Professional & scientific | 2015 |
| JCJ Mortgages Ltd | Financial services | 2023 |
| JDB Driving Services Ltd | Transport & logistics | 2025 |
| JDM Roofing Ltd | Construction | 2024 |
| JE Technical Limited | Construction | 2021 |
| JEB UK Limited | Wholesale & retail | 2005 |
| Jelley Plant Hire Limited | Administrative & support | 2021 |
| Jelly Roll Management Ltd | Real estate | 2012 |
| Jenny Juice Ltd | Manufacturing | 2020 |
| Jensen Racing Limited | Professional & scientific | 2017 |
| Jericho Rose Limited | Hospitality | 2022 |
| JET Propulsion Systems Ltd | Professional & scientific | 2009 |
| JGD Imaging Ltd | Health & social care | 2024 |
| JH Property Associates Ltd | Real estate | 2022 |
| JHG Anaesthesia Limited | Health & social care | 2023 |
| JK Commerce Ltd | Wholesale & retail | 2018 |
| Jmrt Properties Ltd | Real estate | 2020 |
| JNA Contracts Ltd | Construction | 2023 |
| Joedan Holdings Limited | Professional & scientific | 1997 |
| Joedan Manufacturing (U.K.) Limited | Manufacturing | 1985 |
| Johnston Property Renovations Limited | Real estate | 2025 |
| Joka Films Limited | Information & communication | 2010 |
| Jonathan Hodges Limited | Administrative & support | 2014 |
| Jones & Robertson Property Services Ltd | Construction | 2024 |
| Jormae Pourri Limited | Manufacturing | 2015 |
| Jovil Enterprises Ltd | Manufacturing | 2021 |
| Joyndup Ltd | Information & communication | 2017 |
| JPP Group Holdings Ltd | Construction | 2020 |