| Iris Essence Ltd | Financial services | 2025 |
| Irish Gulf Contracting Limited | Construction | 2018 |
| Irish Leather Distributors Limited | | 1945 |
| Irmak Northampton Limited | Hospitality | 2026 |
| Iron & Oak Taverns Ltd | Hospitality | 2025 |
| Iron Bull Groundworks Ltd | Professional & scientific | 2026 |
| Iron Global Property Ltd | Real estate | 2018 |
| Ironcraft of Earl Shilton Ltd | Manufacturing | 2001 |
| Ironlink Callpoint Ltd | Wholesale & retail | 2025 |
| Irons and Kettles Limited | Wholesale & retail | 2019 |
| Irons Holdings Ltd | Real estate | 2024 |
| Ironstone UK Limited | Real estate | 1992 |
| Ironwatch Security Ltd | Administrative & support | 2025 |
| Ironwheelmotors Ltd | Wholesale & retail | 2026 |
| IRR Associates Ltd | Professional & scientific | 2008 |
| Irresistible Group Limited | Professional & scientific | 2015 |
| Irthlingborough Properties Limited | Real estate | 2003 |
| Irvine Group Limited | Administrative & support | 2007 |
| Irving and Irving Associates Limited | Other services | 2007 |
| Irvs Limited | Real estate | 2025 |
| IRW IT Solutions Limited | Information & communication | 2012 |
| IRY House Construction Ltd | Construction | 2025 |
| Iryna Harbuzyuk Ltd | Real estate | 2023 |
| IS Connect Ltd | Construction | 2026 |
| ISA Contructors Ltd | Construction | 2026 |
| Isae Investment Ltd | Real estate | 2025 |
| Isak Tiling Ltd | Construction | 2021 |
| Isbal Limited | Other services | 2019 |
| Iscoyd Michaels Limited | Real estate | 2024 |
| ISE Lodge (2020) Ltd | Health & social care | 2020 |
| Isell Communications Ltd | Administrative & support | 2020 |
| Ishaka Care 2025 Limited | Health & social care | 2025 |
| Ishewedenga(Iwd) Holdings Trading AS Kumbafoods Ltd | Hospitality | 2025 |
| Ishfa Ltd | Education | 2026 |
| Ishika Consultancy Limited | Administrative & support | 2018 |
| Ishopallday Limited | Wholesale & retail | 2022 |
| Isis Mortgages & Finance Ltd | Financial services | 2006 |
| ISL Health Direct Limited | Health & social care | 2015 |
| ISL Refrigeration (Cambs) Ltd | Manufacturing | 2017 |
| Isla Group Limited | Hospitality | 2025 |
| Islam Brothers Investments Limited | Financial services | 2025 |
| Island Beds Ltd | Other services | 2024 |
| Island Vape UK Ltd | Other services | 2015 |
| Island Vybz Limited | Hospitality | 2025 |
| ISM Homes Ltd | Real estate | 2024 |
| ISM Seats Europe Ltd | Professional & scientific | 2007 |
| Ismail Hamed Ltd | Construction | 2026 |
| Isobel a Brown Limited | Professional & scientific | 2004 |
| Isolead Consultants Ltd | Professional & scientific | 1994 |
| Ison Xperiences UK Limited | Administrative & support | 2022 |
| Isorropia Limited | Education | 2014 |
| Isot Limited | Hospitality | 2019 |
| Isource Direct Limited | Professional & scientific | 2014 |
| Issy Clarke Media Ltd | Information & communication | 2019 |
| Istanbul Diamond Limited | Manufacturing | 2023 |
| Istok Retreat Festival CIC | Arts & recreation | 2025 |
| Istrate JET Wash Services Ltd | Construction | 2025 |
| Istrate Limited | Construction | 2018 |
| Isupply Group WLS Ltd | Professional & scientific | 2019 |
| ISV Brickwork Ltd | Construction | 2026 |
| Isybaby Limited | Health & social care | 2022 |
| IT Leading Solutions Ltd | Information & communication | 2021 |
| IT Options Limited | Information & communication | 2019 |
| It's a Birds Thing Ltd | Wholesale & retail | 2024 |
| It's Alarming Limited | Administrative & support | 1998 |
| It's Your Kitchen Ltd | Hospitality | 2019 |
| It-Space Ltd | Information & communication | 2024 |
| Itadelivery Ltd | Transport & logistics | 2024 |
| Ital Maintain Ltd | Other services | 2009 |
| Itarus Limited | Professional & scientific | 1994 |
| ITARUS3 Ltd | Extraterritorial | 2014 |
| Itcc International Ltd | Professional & scientific | 2009 |
| Iteachpro Ltd | Education | 2025 |
| Itemoffice Limited | Construction | 1993 |
| Itgenerationx Ltd | Information & communication | 2025 |
| Itia Ltd | Transport & logistics | 2026 |
| ITS a Gift Limited | Wholesale & retail | 1959 |
| ITS African Sunset Limited | Information & communication | 2014 |
| ITS Interiors Limited | Construction | 2009 |
| Iueg Ltd | Information & communication | 2013 |
| Iulidar Ltd | Transport & logistics | 2020 |
| Iulistone Ltd | Construction | 2017 |
| Iutrans Ltd | Transport & logistics | 2019 |
| Ivaldi Payroll Solutions Ltd | Professional & scientific | 2020 |
| Ivan Dzharakov Logistics Ltd | Transport & logistics | 2019 |
| Ivan Logistics Ltd | Transport & logistics | 2019 |
| Ivan Poparcea Limited | Transport & logistics | 2014 |
| Ivan's Delivery Ltd | Transport & logistics | 2022 |
| IVG Motors Limited | Wholesale & retail | 2018 |
| Ivontek Limited | Wholesale & retail | 2016 |
| Ivory & Obsidian Ltd | Manufacturing | 2022 |
| Ivory and Olive Ltd | Real estate | 2021 |
| Ivory and Onyx Ltd | Other services | 2026 |
| Ivory Business Solutions Ltd | Professional & scientific | 2005 |
| Ivory Topaz Event Ltd | Hospitality | 2026 |
| Ivory Vault Competitions Ltd | Arts & recreation | 2026 |
| Ivory-Owens Consulting Ltd | Information & communication | 2011 |
| Ivstitia Limited | Information & communication | 2022 |
| IVY & B Healthcare Limited | Administrative & support | 2015 |
| IVY and Oak Event Hire LLP | | 2022 |