| Ignite Youth Theatre Ltd | Arts & recreation | 2025 |
| IGS Automation Ltd | Manufacturing | 2019 |
| IJ Holdings Limited | Administrative & support | 2020 |
| IKB Solutions Ltd | Information & communication | 2014 |
| Imara Brands Ltd | Wholesale & retail | 2021 |
| Imara Holdings Ltd | Real estate | 2018 |
| Impact Finance Director Limited | Financial services | 2009 |
| Imperial Aesthetics Limited | Health & social care | 2018 |
| Imperial Properties (Harrow) Limited | Real estate | 2016 |
| Imperio Limited | Transport & logistics | 2009 |
| Imperium Apis Limited | Hospitality | 2023 |
| Impetus Training Ltd | Education | 2010 |
| IN Bocca AL Lupo Limited | Hospitality | 2023 |
| Incuhub Limited | Other services | 2017 |
| Indu Technologies Limited | Information & communication | 2011 |
| Inet Resources Limited | Information & communication | 2026 |
| Infinicell BIO Limited | Professional & scientific | 2025 |
| Infogain Technologies Ltd | Information & communication | 2012 |
| Infosonic Limited | Real estate | 2010 |
| Innova Business Consulting Limited | Information & communication | 2009 |
| Innovantage Consulting Limited | Information & communication | 2024 |
| Innovatax Ltd | Information & communication | 2024 |
| Innoveo Limited | Professional & scientific | 2007 |
| Innoveo Property Management Ltd | Real estate | 2024 |
| Insia Ltd | Wholesale & retail | 2021 |
| Inside Management Ltd | Real estate | 2021 |
| Insight Electrical Contractors Limited | Construction | 2013 |
| Inspire (Kilburn) Limited | Health & social care | 2011 |
| Inspire Management Services Limited | Health & social care | 2011 |
| Instrui Ltd | Information & communication | 2015 |
| Integra Accounts Ltd | Professional & scientific | 2025 |
| Intellections Ltd | Information & communication | 2020 |
| Intelligent Financial Planning Limited | Financial services | 2004 |
| Intelligent Property Group (U.K.) Limited | Real estate | 2025 |
| Intelliserve Consultancy Limited | Information & communication | 2025 |
| Interstones Group Limited | Wholesale & retail | 2022 |
| Intrepid Advisors Limited | Professional & scientific | 2019 |
| Inventory Application Solutions Limited | Real estate | 2011 |
| Investment Consultants Ltd | Financial services | 2013 |
| Investment Corp UK Limited | Real estate | 2017 |
| Investment Partnership LLP | | 2010 |
| Investors in Software | Extraterritorial | 2005 |
| Invicta Software Limited | Information & communication | 2022 |
| IQ Aluminium Limited | Manufacturing | 2015 |
| IQ Glass Group Holdings Limited | Financial services | 2020 |
| IQ Glass Group Ltd | Manufacturing | 2019 |
| IQ Glass Solutions Limited | Manufacturing | 2010 |
| IQ Glass Trustee Limited | Administrative & support | 2024 |
| IQ Outdoor Living Limited | Wholesale & retail | 2016 |
| IQ Tech Consultancy Limited | Information & communication | 2024 |
| IR2R Ltd | Professional & scientific | 2016 |
| Iridium Capital Limited | Financial services | 2026 |
| Ironclad Performance Ltd | Arts & recreation | 2024 |
| IRV Infotech Limited | Information & communication | 2000 |
| Ishaan Consultancy Services Ltd | Information & communication | 2011 |
| Isla and Fraser Ltd | Wholesale & retail | 2019 |
| Isquare Consultancy Ltd | Information & communication | 2016 |
| Isquare Holding Ltd | Real estate | 2021 |
| Ista Technologies Ltd | Information & communication | 2017 |
| It-Venture Holdings Limited | Financial services | 2019 |
| Ivan Donn Consulting Limited | Professional & scientific | 2016 |
| Iver Technical Ltd | Construction | 2025 |
| Iver Technical Services Limited | Professional & scientific | 1991 |
| IVF Chelsea Limited | Health & social care | 2013 |
| IWC Events Limited | Administrative & support | 2024 |
| IWC Media Group Ltd | Professional & scientific | 2025 |
| Izinga Solutions Ltd | Information & communication | 2019 |
| Izzo Good Ltd | Hospitality | 2013 |
| J & D Clark Ltd | Professional & scientific | 2014 |
| J Bros (Investments) Limited | Financial services | 2019 |
| J M Dunne Limited | Real estate | 1978 |
| J&L Peters Properties Ltd | Real estate | 2020 |
| J.A.S.P. South Ltd | Real estate | 2016 |
| J.M. Metal Holdings Limited | Administrative & support | 1992 |
| J2L Limited | Information & communication | 2006 |
| Jaahnu Solutions Limited | Information & communication | 2010 |
| JACK13VFX Limited | Information & communication | 2021 |
| Jacr&Ko Limited | Professional & scientific | 2020 |
| Jaguarsport Limited | Manufacturing | 1997 |
| Jake LEE Media Ltd | Wholesale & retail | 2018 |
| Jakpon Limited | Administrative & support | 2013 |
| Jamie Zwaig Limited | Information & communication | 2007 |
| Jansi Ltd | Information & communication | 2019 |
| Jarokaan Ltd | Professional & scientific | 2021 |
| JAT Mobile Bar Ltd | Hospitality | 2025 |
| Jatayu Holdings Limited | Wholesale & retail | 2025 |
| Javia Limited | Real estate | 2013 |
| Jayanand Estates Limited | Real estate | 2022 |
| JBM Estates Limited | Real estate | 2025 |
| JBULL-P8 Ltd | Information & communication | 2025 |
| JDA Topco Limited | Professional & scientific | 2020 |
| Jda&I Home Limited | Professional & scientific | 2021 |
| JEM Media Ventures Limited | Professional & scientific | 2024 |
| Jesper Design Studio Ltd | Professional & scientific | 2025 |
| Jester GRP Ltd | Wholesale & retail | 2023 |
| Jewlux Company Limited | Wholesale & retail | 2024 |
| JGJ Amsam Ltd | Real estate | 2023 |
| Jimmys Grab Services Limited | Transport & logistics | 2011 |
| Jiya Associates Limited | Professional & scientific | 2011 |
| JJ Maintenance Ltd | Real estate | 2025 |