| ICT Estate Management Limited | Real estate | 2016 |
| ID Business Solutions Limited | Information & communication | 1989 |
| Idea First Limited | Information & communication | 2025 |
| Ideal Property Services (Woking) Limited | Other services | 2015 |
| Ideas on Wheels Ltd. | Professional & scientific | 2013 |
| Idiomatica Limited | Information & communication | 2011 |
| Idlestone Properties (Merrow) Limited | Real estate | 2011 |
| Idli Solutions Limited | Information & communication | 2017 |
| Idox Geospatial Ltd | Information & communication | 2000 |
| Idox PLC | Financial services | 2000 |
| Idox Software Ltd | Information & communication | 1994 |
| Idox Trustees Limited | Professional & scientific | 2000 |
| Idrees Medical Limited | Health & social care | 2021 |
| Idrive Car Hire Ltd | Administrative & support | 2016 |
| Idurmak Limited | Professional & scientific | 2012 |
| IEA Logistics Ltd | Transport & logistics | 2025 |
| IF SO BE Ltd | Information & communication | 2022 |
| Iffley Road Flat Management Limited | Real estate | 2014 |
| Ignite Feature Ltd | Professional & scientific | 2026 |
| Igreja Evangelica Alianca COM Deus | Other services | 2016 |
| Ihlara Restaurant Limited | Hospitality | 2022 |
| Ihome Assets Ltd | Real estate | 2022 |
| Ihtisham Limited | Wholesale & retail | 2025 |
| Ijan Ltd | Transport & logistics | 2021 |
| Ijetel UK Limited | Information & communication | 2012 |
| Ilanda Ltd | Professional & scientific | 2020 |
| Ilex Cottage and Ilex Court Management Company Limited | Real estate | 2017 |
| ILK Film and Television Ltd | Information & communication | 2015 |
| Illume Productions Limited | Information & communication | 2021 |
| Ilumos Development Ltd | Construction | 2025 |
| Ilumos Property (1) Limited | Real estate | 2021 |
| Ilumos Property Development Limited | Construction | 2025 |
| IM a Frog Limited | Professional & scientific | 2026 |
| IMA IMA Foods Ltd | Manufacturing | 2020 |
| Image 22 Fitters Ltd | Manufacturing | 2013 |
| Image 22 Ltd | Manufacturing | 2013 |
| Image Pro-Tech Ltd | Other services | 2018 |
| IMAGE22 Interior Designers Ltd | Manufacturing | 2013 |
| IMAGE22 Investment Ltd | Other services | 2016 |
| Imaginatio Ltd | Manufacturing | 2021 |
| Imagination Glazing Limited | Construction | 2023 |
| Imago DEI Property Holdings Limited | Real estate | 2021 |
| Iman Optical Limited | Health & social care | 2025 |
| Imber Mansions Limited | Households | 1999 |
| Imeld Holdings Ltd | Information & communication | 2024 |
| IML Interactive UK Limited | Information & communication | 2010 |
| Immaculate Chauffeuring Services Limited | Other services | 2008 |
| Immj Ltd | Construction | 2025 |
| Imol Holdings Ltd | Real estate | 2017 |
| Imos Ltd. | Information & communication | 1992 |
| Impact Food Group Limited | Financial services | 2022 |
| Impact Food Topco Limited | Hospitality | 2017 |
| Imperial Car Service Surrey Ltd | Transport & logistics | 2022 |
| Imperial Memorials Ltd | Other services | 2020 |
| Imperium Adventures Ltd | Arts & recreation | 2018 |
| Imperium Interior Solutions Limited | Construction | 2024 |
| Imposed Solutions Limited | Construction | 1996 |
| Impressions Beauty Salon Ltd | Other services | 2008 |
| Imprimis Technology Services Limited | Information & communication | 2003 |
| Improv-Tec Ltd | Professional & scientific | 2013 |
| Improved Finance Limited | Professional & scientific | 2021 |
| Improving YOU Ltd | Wholesale & retail | 2025 |
| Impsynd Software Limited | Information & communication | 2021 |
| Impulse Convenience Ltd | Wholesale & retail | 2021 |
| IN a Pickle (UK) Ltd | Other services | 2012 |
| IN Search of ME Ltd | Information & communication | 2010 |
| IN the Black Solutions Limited | Professional & scientific | 2005 |
| IN the Nick of Time (Woking) Limited | Administrative & support | 2022 |
| IN Touch Property Services Ltd | Administrative & support | 2010 |
| IN Villages Ltd | Real estate | 2009 |
| Inadvia Limited | Information & communication | 2016 |
| Inara Homes Ltd | Real estate | 2016 |
| Inara Interiors Limited | Professional & scientific | 2014 |
| Inbucon Limited | Administrative & support | 1986 |
| Inbuilt Creative Limited | Information & communication | 2017 |
| Incline Design Ltd | Professional & scientific | 2024 |
| Incredible Little Functions Ltd | Hospitality | 2022 |
| Independent Food Group Ltd | Hospitality | 2022 |
| Independent Project Analysis Limited | Professional & scientific | 1998 |
| Independent Travel Experts Limited | Administrative & support | 2011 |
| Indexnine Technologies UK Ltd | Information & communication | 2025 |
| Indi Ruprah Limited | Wholesale & retail | 2012 |
| Indigo Marketing Solutions Limited | Professional & scientific | 2026 |
| Indirect Channel Ltd | Professional & scientific | 1997 |
| Indonesia Power Holdings Limited | Professional & scientific | 1996 |
| Inducon (Westminster) Limited | Construction | 1970 |
| Industrial & Welding Supplies (North West) Ltd | Extraterritorial | 1998 |
| Industrial Supplies & Services Limited | Professional & scientific | 1981 |
| Industry Plumbing Limited | Construction | 2024 |
| Infinigate UK & Ireland Ltd | Wholesale & retail | 1983 |
| Infinite Curiosity Ltd | Extraterritorial | 2012 |
| Infinity Deluxe Group Ltd | Transport & logistics | 2024 |
| Infinity Express Ltd | Wholesale & retail | 2025 |
| Influenced Records Ltd | Wholesale & retail | 2021 |
| Infodec Limited | Information & communication | 1995 |
| Inform Communications Ltd | Information & communication | 1991 |
| Information Tech Limited | Information & communication | 2024 |
| Informcare Limited | Administrative & support | 2013 |
| Infotechnica Limited | Wholesale & retail | 2005 |
| Infrastructure Asset Development Services Limited | Professional & scientific | 2012 |