| International Educational Pathways UK Limited | Administrative & support | 2025 |
| International Full Gospel Fellowship (Ifgf) UK Limited | Other services | 2017 |
| International Godly People Ltd | Other services | 2025 |
| International London Academy Ltd. | Administrative & support | 2018 |
| International Marketing Corporation Limited | Wholesale & retail | 1993 |
| International Paint Limited | Manufacturing | 1899 |
| International Paints (Holdings) Limited | Professional & scientific | 1908 |
| International Power Monitoring Ltd | Professional & scientific | 2021 |
| International Studywise Ltd | Other services | 2021 |
| International Youth Speaking Festival Ltd | Education | 2026 |
| Internzity Ltd | Information & communication | 2025 |
| Interpost Ltd. | Transport & logistics | 1993 |
| Intervene Asset Investments Ltd | Real estate | 2004 |
| Interview Skills Academy Ltd | Education | 2016 |
| Intex Yarns (Manufacturing) Limited | Professional & scientific | 1914 |
| Intignis Designs Ltd. | Wholesale & retail | 2018 |
| Intiki Limited | Wholesale & retail | 2023 |
| Into Peru Limited | Administrative & support | 2015 |
| Intouch Technical Services Limited | Professional & scientific | 2018 |
| Intravit Global Ltd | Health & social care | 2023 |
| Intuition PYP Limited | Education | 2019 |
| Intuitive Asset Holdings Limited | Financial services | 2021 |
| Intuteach Limited | Education | 2025 |
| Inula Holding UK Limited | Administrative & support | 1995 |
| Invc Management Limited | Professional & scientific | 2014 |
| Inveniam Production Ltd | Other services | 2015 |
| Inveniam Properties Ltd | Real estate | 2021 |
| Inventive Homes Ltd | Real estate | 2024 |
| Inventive Networks Ltd | Information & communication | 2019 |
| Invested in UK Ltd | Professional & scientific | 2003 |
| Investix Corporation Limited | Financial services | 2022 |
| Invincible Productions Ltd | Arts & recreation | 2014 |
| Invotec Retail Ltd | Wholesale & retail | 2025 |
| Inwego Ltd | Other services | 2022 |
| Inyat Limited | Transport & logistics | 2026 |
| INZ Technologies UK Ltd | Information & communication | 2019 |
| IO Holdings Limited | Real estate | 2022 |
| Ioana&Cornelia's Homemade Cakes Limited | Manufacturing | 2019 |
| Iofitness Limited | Wholesale & retail | 2020 |
| Ionetiq Limited | Information & communication | 2020 |
| Ionomer Ltd | Financial services | 2024 |
| IP Bulls Limited | Financial services | 2024 |
| IP Consulting Firm Ltd | Information & communication | 2025 |
| IP Insight Limited | Information & communication | 2008 |
| IPS Estates Ltd | Real estate | 2018 |
| Ipyro SFX Ltd | Information & communication | 2026 |
| IQ Home Improvements Ltd | Construction | 2018 |
| IQ Mart Limited | Information & communication | 2025 |
| Iqms (Inspection Quality Management Services) Limited | Construction | 2007 |
| Iqoniqa Ltd | Real estate | 2023 |
| Iqra Islamic Society | Education | 1998 |
| IR IT Consultancy Services Limited | Information & communication | 2021 |
| Irec Resourcing Ltd | Administrative & support | 2006 |
| Ireland FX Ltd | Financial services | 2004 |
| Ireland Indian Entertainments UK Limited | Information & communication | 2023 |
| Irfonomics Ltd | Wholesale & retail | 2025 |
| Irftech Consulting Ltd | Information & communication | 2025 |
| Iris Bidco Limited | Financial services | 2018 |
| Iris Business Software Limited | Information & communication | 1986 |
| Iris Canada Holdings Limited | Administrative & support | 2021 |
| Iris Capital Limited | Administrative & support | 2007 |
| Iris Conex Ltd | Wholesale & retail | 2022 |
| Iris Debtco Limited | Financial services | 2018 |
| Iris Education Limited | Information & communication | 2025 |
| Iris Education Payroll Limited | Administrative & support | 2025 |
| Iris Education Software Limited | Information & communication | 2025 |
| Iris Firm Management Limited | Information & communication | 2014 |
| Iris Group Limited | Information & communication | 1996 |
| Iris Holdings Limited | Extraterritorial | 2000 |
| Iris Midco Limited | Financial services | 2018 |
| Iris Payroll Services Limited | Information & communication | 2011 |
| Iris Payroll Solutions Limited | Information & communication | 1984 |
| Iris Resourcing Limited | Professional & scientific | 2007 |
| Iris Software Group Limited | Extraterritorial | 2007 |
| Iris Software Limited | Information & communication | 1996 |
| Iris US Holdings Limited | Administrative & support | 2021 |
| Irlondon Limited | Construction | 2024 |
| Irmy Transport Ltd | Transport & logistics | 2024 |
| Iron Lock Civil Engineering & Security Services Ltd | Administrative & support | 2022 |
| Iron River Limited | Professional & scientific | 2008 |
| Ironridge Advisory Ltd | Information & communication | 2026 |
| IRS Consulting Limited | Professional & scientific | 2009 |
| Irus Consulting Ltd | Information & communication | 2013 |
| Irvine Thanvi Natas Limited | Professional & scientific | 2010 |
| IS Places Limited | Hospitality | 2021 |
| IS Pros Limited | Professional & scientific | 2021 |
| Isamk Ltd | Health & social care | 2026 |
| Isams Limited | Information & communication | 2005 |
| Isavasyam Properties Ltd | Real estate | 2026 |
| ISB Design & Print Ltd | Professional & scientific | 2026 |
| ISE Aviation Services Limited | Transport & logistics | 2023 |
| Isea Construction Ltd | Construction | 2023 |
| Isea Property Development Ltd | Real estate | 2023 |
| ISH Homes Ltd | Real estate | 2023 |
| Isha Foundation | Health & social care | 2010 |
| Ishai Limited | Financial services | 2016 |
| Ishalife Limited | Other services | 2021 |
| Ishani Gordon Interiors Limited | Construction | 2017 |
| Ishanvi Consulting Services Ltd | Information & communication | 2024 |
| Ishtech Ltd | Wholesale & retail | 2023 |