| Inside OUT Construction Limited | Construction | 2007 |
| Insight Medical Consultancy Ltd | Financial services | 2019 |
| Insight Plum Limited | Information & communication | 2020 |
| Inspiration in Leadership Limited | Information & communication | 2023 |
| Inspirations Hair Salon Limited | Other services | 2011 |
| Inspire Advertising Limited | Professional & scientific | 2005 |
| Inspire Care Agencies Limited | Health & social care | 2017 |
| Inspire Care Franchise Limited | Health & social care | 2019 |
| Inspire Drinks Ltd | Wholesale & retail | 2014 |
| Instar Services Ltd | Administrative & support | 2008 |
| Instataxi Ltd | Transport & logistics | 2026 |
| Institute for Quantitative Investment Research | Other services | 1989 |
| Instrument Engineering Services Limited | Real estate | 1986 |
| Insymphony Marketing Ltd | Professional & scientific | 2018 |
| Intara Ltd | Education | 2025 |
| Intavision Services Limited | Administrative & support | 2018 |
| Integer Consulting Ltd | Professional & scientific | 2023 |
| Integrated Holistic Medical Care Limited | Health & social care | 2019 |
| Integrated Yard Services Limited | Other services | 2026 |
| Integro Surgical Limited | Health & social care | 2020 |
| Intelion Energy Group Limited | Professional & scientific | 2023 |
| Intelligent Profile LLP | | 2006 |
| Intelligent Steps Limited | Administrative & support | 2018 |
| Inter-Leisure Limited | Real estate | 1978 |
| Interfaced Technologies Ltd | Information & communication | 2020 |
| Interiors Media Limited | Information & communication | 2007 |
| International Association for Forensic Psychotherapy Ltd | Other services | 2013 |
| International Catalogue Raisonné Association | Other services | 2021 |
| Intrapreneur Secrets Ltd | Information & communication | 2024 |
| Inventorsspace Ltd | Information & communication | 2012 |
| Investeco Overseas Holdings Limited | Financial services | 1970 |
| Investsure Holdings Ltd | Financial services | 2015 |
| Invicta Business Holdings Limited | Financial services | 2016 |
| Invicta Electrical Ltd | Extraterritorial | 2021 |
| Invicta Express Limited | Information & communication | 1991 |
| Invicta Heating Ltd | Construction | 2020 |
| Invicta Spray Chrome Ltd | Professional & scientific | 2020 |
| Invicta Weeds Limited | Administrative & support | 2006 |
| Invictus Electrical Solutions Ltd | Construction | 2024 |
| Inzinc Consulting Limited | Information & communication | 2013 |
| Iona Communications Limited | Professional & scientific | 2004 |
| Ionichem Ltd | Professional & scientific | 2016 |
| IOS Consulting Ltd | Information & communication | 2006 |
| IP Building Ltd | Construction | 2023 |
| IPL 1 Limited | Real estate | 2022 |
| Iqual Limited | Information & communication | 1991 |
| Iraam Property 1 Ltd | Real estate | 2025 |
| Irbis Energy Group Ltd | Mining & quarrying | 2023 |
| Ironmanmadmax UK Services Limited | Administrative & support | 2017 |
| Irvine Property Solutions Limited | Real estate | 2015 |
| Is-Instruments Limited | Professional & scientific | 2010 |
| Isabella Shopper Limited | Wholesale & retail | 2025 |
| Isaida Consulting Limited | Professional & scientific | 2023 |
| Iseli Media Ltd | Information & communication | 2024 |
| ISN UK Security Ltd | Administrative & support | 2019 |
| Isova Limited | Information & communication | 2020 |
| IT Datastore Solutions Limited | Information & communication | 2010 |
| IT Europa Momentum Ltd | Administrative & support | 2016 |
| It.Ally Limited | Information & communication | 2009 |
| Itrust Partnering Limited | Administrative & support | 2016 |
| Itsekiri Congress UK Ltd | Education | 2020 |
| ITX 42 Limited | Professional & scientific | 2022 |
| J & G Smallcombe Limited | Wholesale & retail | 2012 |
| J & H Accounting Services Limited | Professional & scientific | 2002 |
| J Beresford Consulting Ltd | Information & communication | 2019 |
| J Dickinson Consulting Limited | Administrative & support | 2008 |
| J F Metal Recycling Ltd | Water & waste | 2026 |
| J F Yacht Sales & Charter Ltd | Wholesale & retail | 2022 |
| J Farrow Services Ltd | Construction | 2013 |
| J Greer Limited | Construction | 2017 |
| J Mcpherson Legal Costing Limited | Professional & scientific | 2015 |
| J Morgan Property Limited | Construction | 2013 |
| J Penfold Heating & Plumbing Limited | Construction | 2011 |
| J S Gregory Ltd | Professional & scientific | 2011 |
| J S Taylor Electrical Ltd. | Construction | 2011 |
| J Thurston & Co Ltd | Manufacturing | 2025 |
| J W Roofing & Guttering Solutions Ltd | Construction | 2026 |
| J&J Chrysalis Ltd | Health & social care | 2017 |
| J&M Health Ltd | Health & social care | 2019 |
| J. & R. Killick Limited | Extraterritorial | 2024 |
| J.A.A. Comms Ltd | Information & communication | 2017 |
| J.A.I Group Ltd | Construction | 2023 |
| J.C. Romic Ltd. | Real estate | 1999 |
| J.M.D Scaffolding Ltd | Construction | 2020 |
| J.W. Timber Ltd | Wholesale & retail | 2003 |
| JA Capital Investments Limited | Financial services | 2024 |
| JAC 2015 Ltd | Other services | 2015 |
| JAC Anaesthetics Ltd | Health & social care | 2019 |
| JAC Health Ltd | Health & social care | 2021 |
| Jacamel Limited | Financial services | 2020 |
| Jack Charles Property Services Limited | Real estate | 2019 |
| Jack Henry Cars Limited | Wholesale & retail | 2013 |
| Jackie Dickins Limited | Professional & scientific | 2003 |
| Jackpot Technology Limited | Wholesale & retail | 1996 |
| Jacob Oliver Associates Limited | Professional & scientific | 2019 |
| Jacqueline Hartley Limited | Education | 2017 |
| Jadco Group Ltd | Financial services | 2022 |
| Jadco Shipping Ltd | Transport & logistics | 2022 |
| JAI Edtech Ltd | Education | 2026 |
| JAK Colgate Design Ltd | Professional & scientific | 2021 |