| Iredia Resources Limited | Construction | 2025 |
| Ireland Ekonomi Office Limited | Professional & scientific | 2022 |
| Iremos Limited | Wholesale & retail | 2021 |
| Irfancom UK Ltd | Information & communication | 2023 |
| IRI Plumbing Ltd | Construction | 2026 |
| Iridium DS UK Ltd | Information & communication | 2025 |
| Irinel Cojoc Removals Limited | Transport & logistics | 2025 |
| Iris Automotive Ltd | Information & communication | 2021 |
| Iris Financial Services Ltd | Financial services | 2019 |
| Iris Properties & Lettings Ltd | Real estate | 2025 |
| IRK Limited | Health & social care | 2013 |
| Irlcc Limited | Information & communication | 2007 |
| Irly Holding AS Limited | Financial services | 2026 |
| Irly Holding BB Limited | Financial services | 2026 |
| Irly Holding TG Limited | Financial services | 2026 |
| Irly Limited | Information & communication | 2023 |
| IRM Commercial Services Limited | Professional & scientific | 2014 |
| Iroko Carpentry and Joinery Ltd | Construction | 2014 |
| Iron Armory Ltd | Wholesale & retail | 2026 |
| Iron Coat Ltd | Wholesale & retail | 2026 |
| Iron Mill (IT) Limited | Information & communication | 2022 |
| Iron Recruit Ltd | Administrative & support | 2026 |
| Iron Stag Ltd | Manufacturing | 2023 |
| Iron Tiger Bramhope Limited | Hospitality | 2025 |
| Iron Tiger Coffee Co Limited | Hospitality | 2024 |
| Ironbridge International Limited | Professional & scientific | 2009 |
| Ironkill Ltd | Information & communication | 2023 |
| IRP Realisations Limited | Manufacturing | 1986 |
| Irradiated Hound Entertainment Limited | Manufacturing | 2016 |
| Irrawaddy Limited | Health & social care | 2025 |
| Irtza Ltd | Wholesale & retail | 2021 |
| IRU07 Ltd | Real estate | 2018 |
| Irving Knight Group Holdings Ltd | Financial services | 2024 |
| Irving Knight Group Limited | Administrative & support | 2019 |
| IRW Engineering & Electrical Ltd | Construction | 2024 |
| Irwin Mitchell Limited | Extraterritorial | 2009 |
| Irwin Steele Construction Ltd | Construction | 2019 |
| IS601 Ltd | Real estate | 2024 |
| ISA Investments Ltd | Real estate | 2018 |
| ISA UK Holdings Ltd | Real estate | 2025 |
| Isaac (U.K.) | Health & social care | 1985 |
| Isaac a Ltd | Wholesale & retail | 2016 |
| Isaac's Transport Ltd | Transport & logistics | 2023 |
| Isaak Mellor LLP | | 2017 |
| Isabel's Cuisine Limited | Wholesale & retail | 2005 |
| Isabi Ltd | Wholesale & retail | 2025 |
| Isalba Properties Limited | Construction | 2017 |
| Isamz Properties Ltd | Real estate | 2025 |
| ISC Civil and Structural Consulting Engineers Ltd | Professional & scientific | 2009 |
| ISC Concrete Ltd | Manufacturing | 2015 |
| ISC Future Finance Ltd | Financial services | 2023 |
| ISC Ltd | Education | 2026 |
| Ischedule 365 Limited | Administrative & support | 2025 |
| ISE Vale Medical Services Ltd | Other services | 2014 |
| Iseepr Digital Limited | Extraterritorial | 2022 |
| Iseepr Limited | Administrative & support | 2007 |
| ISG Talent Partners Ltd | Information & communication | 2024 |
| ISG Ventures Limited | Administrative & support | 2016 |
| Isha Divine Ltd | Other services | 2025 |
| Ishaq ALI Contractors Ltd | Professional & scientific | 2017 |
| Ishmael Davis Boxing Limited | Real estate | 2024 |
| Ishmaheal & Co Limited | Professional & scientific | 2015 |
| ISI Group of Company Ltd | Construction | 2024 |
| ISI Security Solutions Limited | Extraterritorial | 2024 |
| Isibane Selanga Limited | Health & social care | 2024 |
| Iskcon Foods Limited | Wholesale & retail | 2025 |
| Isla and Smith Events Limited | Other services | 2022 |
| Islamic Divorce & Khula Ltd | Professional & scientific | 2014 |
| Island Caribbean Kitchen Limited | Hospitality | 2026 |
| Island Connect Limited | Administrative & support | 2026 |
| Isle Developments Limited | Construction | 2021 |
| Isle of Wight Energy Network Limited | Construction | 2025 |
| Isle Ventures Limited | Professional & scientific | 2025 |
| Islington Lighting (Finance) Limited | Administrative & support | 2003 |
| ISM Edutech (UK) Ltd | Education | 2019 |
| Ismail Bakhshy Ltd | Transport & logistics | 2025 |
| Ismail Textiles (UK) Limited | Wholesale & retail | 2016 |
| Isman Inc Limited | Health & social care | 2017 |
| Ismart Electrics Limited | Construction | 2020 |
| ISO Energy Limited | Administrative & support | 2006 |
| ISO Photographic Limited | Arts & recreation | 2015 |
| Isofin Properties Limited | Administrative & support | 2017 |
| Isolray Limited | Transport & logistics | 2025 |
| Isomer Ltd | Information & communication | 2018 |
| Isong Medical Services Limited | Health & social care | 2013 |
| Isorobot Limited | Information & communication | 2020 |
| Ispa Academy Ltd | Extraterritorial | 2023 |
| Isra Noor Ltd | Transport & logistics | 2023 |
| Isra Plant Limited | Wholesale & retail | 2026 |
| ISS Building Services Ltd | Construction | 2022 |
| ISS International Ltd | Information & communication | 2007 |
| Issychino Limited | Health & social care | 2013 |
| IST Consultancy Limited | Professional & scientific | 2012 |
| Istanbul Bakery Ltd | Hospitality | 2017 |
| Istanbul CUT Ltd | Other services | 2026 |
| Istanbul Cutz Rothwell Limited | Other services | 2023 |
| Istanbul Leeds Ltd | Hospitality | 2024 |
| IT Grows on YOU Ltd | Professional & scientific | 2024 |
| IT Legal Tech Solutions Limited | Professional & scientific | 2025 |
| IT Only Gets Better Ltd | Information & communication | 2025 |