| IRH Consultancy Solutions Ltd | Professional & scientific | 2019 |
| Irimaging Ltd | Manufacturing | 2011 |
| Iris Fabrication Limited | Manufacturing | 2022 |
| Iris Plumbing Services Limited | Construction | 2025 |
| Iris Rigging Limited | Construction | 2009 |
| Iris Stays Ltd | Real estate | 2025 |
| Irish Anglo Properties Limited | Real estate | 2003 |
| IRL GAS Services Ltd | Extraterritorial | 2022 |
| IRO Borne Ltd | Manufacturing | 2017 |
| Iron Brook Limited | Hospitality | 2019 |
| Iron Chophouse Limited | Hospitality | 2025 |
| Iron Giant Storage Ltd | Transport & logistics | 2026 |
| Ironbond Limited | Extraterritorial | 1992 |
| Ironhide Equine Limited | Wholesale & retail | 2025 |
| Ironmind Productions Ltd | Information & communication | 2024 |
| Ironmongery UK Limited | Wholesale & retail | 2024 |
| Irons & Stone Restoration Limited | Construction | 2007 |
| Ironside Associates Limited | Administrative & support | 2006 |
| Irvine Stanley Limited | Health & social care | 2018 |
| IS Media Group Ltd | Professional & scientific | 2025 |
| IS98 Developments Limited | Administrative & support | 2021 |
| ISA MAE Holdings Ltd | Financial services | 2024 |
| Isaa Construction Ltd | Mining & quarrying | 2017 |
| Isabel James Ltd | Hospitality | 2023 |
| Isabel Odonto Ltd | Health & social care | 2023 |
| Isabellas (South Yorkshire) Ltd | Hospitality | 2023 |
| Isabelle Grafin Grote Limited | Extraterritorial | 2025 |
| Isachar Limited | Administrative & support | 2001 |
| Isai Technologies Ltd | Information & communication | 2002 |
| Isano Property Ltd | Real estate | 2023 |
| Isas Consulting Limited | Information & communication | 2018 |
| Isec Risk Consulting Limited | Information & communication | 2017 |
| ISI Properties Ltd | Real estate | 2023 |
| Isik Barbers Ltd | Other services | 2023 |
| Isinglass Consulting Ltd | Professional & scientific | 2025 |
| Isis Aviation Services Limited | Professional & scientific | 1994 |
| Isis Conveyancing Insurance Specialists Limited | Financial services | 2006 |
| Island Highway & Transport Consultants Limited | Professional & scientific | 2013 |
| Island Sports and Social Club Limited | Arts & recreation | 2025 |
| Islanders Protection Security Services Ltd | Administrative & support | 2018 |
| Isle Architects Ltd | Professional & scientific | 2023 |
| Isle of MAN Container Line (UK) Limited | Transport & logistics | 2003 |
| Isle of Reeds Brewing Company Ltd | Extraterritorial | 2021 |
| Isobel Ford Developments Limited | Construction | 2007 |
| Isobel's Styles for YOU Limited | Wholesale & retail | 2017 |
| Isochemix Limited | Professional & scientific | 2016 |
| Isolate Industries Ltd | Construction | 2020 |
| Ispirare Accessories Limited | Wholesale & retail | 2010 |
| Isport International Projects Limited | Arts & recreation | 2013 |
| IT DIS Consultants Limited | Information & communication | 2017 |
| IT Geeks Group Limited | Information & communication | 2023 |
| IT Norwich Limited | Information & communication | 2016 |
| It's a Monthly Thing Limited | Wholesale & retail | 2013 |
| It's Simply Virtual Limited | Professional & scientific | 2022 |
| IT2DAY Ltd | Wholesale & retail | 2018 |
| Itaewon Korean Hub Ltd | Wholesale & retail | 2022 |
| Italvenice Ltd | Hospitality | 2020 |
| Italy Food Shop Ltd | Wholesale & retail | 2023 |
| Itelica Ltd | Information & communication | 2002 |
| Itfp Fibre Ltd | Construction | 2023 |
| Ithena Group Limited | Administrative & support | 2018 |
| Ithink Media Ltd | Information & communication | 2017 |
| Itlex Ltd | Information & communication | 2026 |
| Itml Information Technology for Market Leadership Ltd | Information & communication | 2023 |
| Itradershouse Ltd | Wholesale & retail | 2013 |
| ITS UK Services Ltd | Transport & logistics | 2016 |
| Itsbeer Limited | Manufacturing | 2023 |
| Itsl Holdings Ltd | Professional & scientific | 2017 |
| Itsl Properties Ltd | Hospitality | 2020 |
| Itte Limited | Information & communication | 2024 |
| Ivan and Paul Fisher Holdings Limited | Real estate | 2018 |
| Ivan Chubbock Garage Services Limited | Wholesale & retail | 2018 |
| Ivan Fisher Independent Funeral Homes Limited | Other services | 2008 |
| Ivan Groom Design & Reports Ltd | Professional & scientific | 2025 |
| Ivanova Ventures Ltd | Professional & scientific | 2022 |
| Ivee Properties Ltd | Real estate | 2021 |
| Ivemy Holdings Ltd | Financial services | 2024 |
| Ives-Keeler Limited | Real estate | 2011 |
| IVI 22 Distribution Ltd | Transport & logistics | 2022 |
| Ivory House Studios Ltd | Information & communication | 2024 |
| IVY Farm (Coddenham) Limited | Agriculture & fishing | 1982 |
| IVY Flats Residents Association Limited | Real estate | 1975 |
| IVY Properties London Limited | Real estate | 2018 |
| Ivy's Decor and Catering Ltd | Hospitality | 2025 |
| Iware Designs Limited | Information & communication | 2010 |
| Iwell UK Limited | Manufacturing | 2025 |
| IWR Media Ltd | Information & communication | 2010 |
| Iyasaka Cafe Ltd | Hospitality | 2024 |
| IZ Services Limited | Administrative & support | 2012 |
| Izyan Holdings Ltd | Financial services | 2023 |
| Izzy Healthcare Services Limited | Health & social care | 2019 |
| Iënit Limited | Health & social care | 2021 |
| J & B Developments Limited | Real estate | 2017 |
| J & B Menswear Limited | Wholesale & retail | 2003 |
| J & D Carpentry Services Ltd | Construction | 2014 |
| J & D Developments (Norfolk) Limited | Extraterritorial | 2015 |
| J & D Kemp Financial Services Ltd | Financial services | 2019 |
| J & D Property Ltd | Real estate | 2017 |
| J & D Snape Limited | Construction | 2014 |
| J & H Sheetmetal Work Ltd | Manufacturing | 2010 |