| International Leisure Limited | Manufacturing | 2011 |
| International Motor Part Supplies Limited | Professional & scientific | 1996 |
| International Parking Systems (UK) Limited | Professional & scientific | 2016 |
| International Platforms Limited | Wholesale & retail | 2020 |
| International Racecourse Management Limited | Arts & recreation | 1991 |
| International Racing Media Limited | Information & communication | 1996 |
| International Sleeper Trains Ltd | Transport & logistics | 2023 |
| Internet Business Management Ltd | Information & communication | 2024 |
| Internet Elephants Ltd | Professional & scientific | 2008 |
| Internetname IP Limited | Professional & scientific | 2011 |
| Intertrain UK (Holdings) Limited | Financial services | 2018 |
| Intertrain UK Ltd. | Education | 2003 |
| Intofocus Limited | Professional & scientific | 2012 |
| Intricut Home Ltd | Professional & scientific | 2024 |
| Invest Global Group Limited | Wholesale & retail | 2025 |
| Invest Yorkshire Limited | Construction | 2017 |
| Invest-In Developments Ltd | Households | 2024 |
| Investmakers Ltd. | Information & communication | 2010 |
| Investment & Finance Ltd | Extraterritorial | 2026 |
| Investment Link UK. Ltd | Administrative & support | 2019 |
| Invincible Results Ltd | Professional & scientific | 2019 |
| Invisible College Limited | Administrative & support | 2006 |
| IOA Developments Limited | Real estate | 2026 |
| Ioan-Marius Living Innovations Ltd | Construction | 2023 |
| ION TEC Ltd | Administrative & support | 2016 |
| Ionescu 2753 Ltd | Manufacturing | 2022 |
| Ionut&Tudor Ltd | Transport & logistics | 2020 |
| IPA Mini Market Ltd | Wholesale & retail | 2021 |
| IPA Property Limited | Real estate | 2025 |
| IPG Classics & Hotrods Ltd | Wholesale & retail | 2024 |
| IPL Electrical Ltd | Construction | 2021 |
| Ippgr Holding Ltd | Financial services | 2018 |
| IPR Shopfitting Ltd | Construction | 2021 |
| Ipwt Ltd | Transport & logistics | 2018 |
| IQ Trans Limited | Administrative & support | 2015 |
| Iqlabs Ltd | Information & communication | 2019 |
| Ir&Zq Limited | Wholesale & retail | 2024 |
| Irimar Taste Ltd | Hospitality | 2023 |
| Iris 2018 Ltd | Transport & logistics | 2018 |
| IRM (Event Safety and Security) Ltd | Administrative & support | 2006 |
| Irom Ltd | Transport & logistics | 2017 |
| Iron Horse Equestrian Supplies Limited | Wholesale & retail | 2007 |
| Iron K9 Training Ltd | Education | 2026 |
| Iron Management Limited | Hospitality | 2015 |
| Ironbeam Construction Ltd | Extraterritorial | 2026 |
| Ironbridge Solutions Ltd | Extraterritorial | 2026 |
| Ironbridge Uniform Ltd | Extraterritorial | 2026 |
| Ironclad Car Care Ltd | Administrative & support | 2026 |
| Ironhaven Fabrication Ltd | Extraterritorial | 2025 |
| Ironlark Transport Ltd | Extraterritorial | 2026 |
| Ironstone Manufacturing Ltd | Extraterritorial | 2026 |
| Ironvale Engineering Ltd | Extraterritorial | 2026 |
| Ironwill Collective Ltd | Extraterritorial | 2026 |
| Ironwood Holdings Ltd | Real estate | 2024 |
| Ironwrench Automotive Ltd | Extraterritorial | 2026 |
| IS Tcomm Limited | Information & communication | 2023 |
| Isaac Transport Ltd | Construction | 2023 |
| Isabell Ltd | Wholesale & retail | 2019 |
| Isaia Toth Ltd | Transport & logistics | 2022 |
| Isaiah Sabah Ltd | Real estate | 2026 |
| Isan Developments Limited | Wholesale & retail | 2022 |
| Iscar Ventures Ltd | Information & communication | 2025 |
| Isevar Holdings Limited | Financial services | 2026 |
| Isevar Projects Limited | Construction | 2026 |
| Ishe Limited | Health & social care | 2016 |
| Ishola Medics Limited | Health & social care | 2012 |
| Ishola Property DOC Limited | Real estate | 2024 |
| Isight at Home Ltd | Health & social care | 2021 |
| Isle Care (Axholme) Ltd | Health & social care | 1999 |
| Isle Communications Group Limited | Professional & scientific | 1995 |
| Isle Construct Ltd | Construction | 2018 |
| Isle Consult Ltd | Construction | 2018 |
| Isle Design - Architecture Ltd | Professional & scientific | 2012 |
| Isle Design and Marketing Limited | Professional & scientific | 1991 |
| Isle Education Trust | Education | 2011 |
| Isle Fleet Support Ltd | Wholesale & retail | 2025 |
| Isle Homeware Ltd | Wholesale & retail | 2025 |
| Isle Installations Ltd | Administrative & support | 2016 |
| Isle of Axholme Rugby Club Ltd | Arts & recreation | 2023 |
| Isle Record IT Ltd | Professional & scientific | 2024 |
| Isle Services (UK) Limited | Construction | 2013 |
| Isle Site Services (UK) Ltd | Manufacturing | 2017 |
| Isle Study Centre Ltd | Education | 2020 |
| Isle Trade Cars Ltd | Wholesale & retail | 2025 |
| Isoplus Piping Systems Limited | Professional & scientific | 2016 |
| ISR BO Ltd | Transport & logistics | 2017 |
| Isso Limited | Hospitality | 2023 |
| Istanbul Barber (Conisbrough) Ltd | Other services | 2023 |
| Istanbul Barber (Dunscroft) Limited | Other services | 2024 |
| Istore (Doncaster) Ltd | Transport & logistics | 2024 |
| Isvac Ltd | Transport & logistics | 2025 |
| IT Assist Services Ltd | Information & communication | 2016 |
| IT Consultancy and Repairs Limited | Information & communication | 2025 |
| IT Services Grimsby Limited | Information & communication | 2016 |
| IT Support Hotline Ltd | Information & communication | 2024 |
| Italian Catering Services Ltd | Hospitality | 2026 |
| Italian LA Rustica Ltd | Hospitality | 2025 |
| Italo Balcanic Limited | Hospitality | 2019 |
| Italo Grand Coffee Limited | Hospitality | 2020 |
| Itech Group Ltd | Wholesale & retail | 2019 |