| Iota Pharmaceuticals Limited | Professional & scientific | 2007 |
| Ioteach Ltd | Professional & scientific | 2016 |
| IOV4AIRCRAFT Ltd | Manufacturing | 2025 |
| Iovan Daniel Aero Space Ltd | Manufacturing | 2026 |
| IP Ltd | Extraterritorial | 2022 |
| IP2 Management Ltd | Professional & scientific | 2021 |
| IP2X Limited | Information & communication | 2026 |
| Ipat Services Limited | Professional & scientific | 2018 |
| Ipc-Nostos Limited | Information & communication | 2025 |
| Iposurvey Co., Ltd | Information & communication | 2017 |
| Ipsec Network IT Consultancy Ltd | Information & communication | 2020 |
| Ipsum Invest Limited | Professional & scientific | 2016 |
| IPV Limited | Manufacturing | 2004 |
| IPX10 Ltd | Information & communication | 1999 |
| Iqgeo Group Limited | Professional & scientific | 2005 |
| Iqgeo UK Limited | Information & communication | 2018 |
| Iquk College Limited | Education | 2013 |
| IR 2018 Limited | Professional & scientific | 2001 |
| Iram Services Limited | Construction | 2003 |
| Ireland Century Blue Ecological Agriculture Technology Limited | Extraterritorial | 2016 |
| Ireland Huskarli Fertilizer Ltd | Mining & quarrying | 2025 |
| Ireland Teoranta Halobios Co., Ltd | Mining & quarrying | 2025 |
| Iridescent Prospect International Co., Ltd | Extraterritorial | 2012 |
| Iris Futures Ltd | Wholesale & retail | 2025 |
| Iris Global UK Limited | Health & social care | 1994 |
| Irisation Ltd | Information & communication | 2015 |
| Irmina Paulina Pala Ltd | Wholesale & retail | 2020 |
| Irof Ltd | Professional & scientific | 2018 |
| Iron Acton Power Limited | Manufacturing | 2021 |
| Iron Crown Enterprises Ltd. | Information & communication | 2009 |
| Ironing Relief Ltd | Other services | 2021 |
| Ironsmith Industries Ltd | Professional & scientific | 2025 |
| Ironstar Engineering Ltd | Manufacturing | 2026 |
| Irvine Baker Associates Ltd. | Other services | 2012 |
| IS IT Helpful? Limited | Other services | 2012 |
| Is-Fla Ltd | Manufacturing | 2017 |
| Is.Io Limited | Other services | 2013 |
| ISA Research Limited | Other services | 2021 |
| Isaac Liberty Limited | Professional & scientific | 2018 |
| Isaacson Associates Ltd | Other services | 2017 |
| Isabella Fernandez Interiors Ltd | Professional & scientific | 2023 |
| Isanna Ltd | Professional & scientific | 2018 |
| ISH Technology Limited | Information & communication | 2016 |
| Ishleez Ltd | Wholesale & retail | 2023 |
| Ishoo Limited | Wholesale & retail | 2021 |
| Iskyline Ltd | Manufacturing | 2024 |
| Isla Babot Consulting Ltd | Professional & scientific | 2023 |
| Isla Babot Holding Ltd | Financial services | 2023 |
| Island Dairies (UK) Limited | Wholesale & retail | 2023 |
| Islay Office Investments | Administrative & support | 2024 |
| Isld Limited | Financial services | 2008 |
| Isle Interactive Limited | Information & communication | 2005 |
| Isle of Pets Ltd | Wholesale & retail | 2016 |
| Islegrove Homes Limited | Real estate | 2016 |
| Islegrove Properties Limited | Real estate | 2014 |
| Islington Gates Birmingham (UK) Ltd | Real estate | 2022 |
| Islington Web Development Limited | Information & communication | 2001 |
| Isobel Harper Counselling Limited | Other services | 2011 |
| Isolon Consultants Ltd | Professional & scientific | 2025 |
| Isomab Ltd | Professional & scientific | 2022 |
| Isomass Ltd | Construction | 2006 |
| Isomerase Therapeutics Limited | Professional & scientific | 2012 |
| Ispek Solutions Ltd | Information & communication | 2018 |
| Isprayanything Ltd | Other services | 2015 |
| Israel Aoshi Biochemical Group Co., Ltd | Wholesale & retail | 2023 |
| Israel Aviv Chemical Group Corporation. Ltd | Mining & quarrying | 2026 |
| Israel Bailiou International Chemical Ltd | Mining & quarrying | 2021 |
| Israel Baindt Chemical International Co., Ltd | Mining & quarrying | 2026 |
| Israel Belim Crop Nutrition Ltd | Mining & quarrying | 2020 |
| Israel Caribbean International Chemical Co., Ltd | Mining & quarrying | 2026 |
| Israel Cologne Crop Nutrition Co., Ltd | Wholesale & retail | 2023 |
| Israel Corolla International Group Ltd | Mining & quarrying | 2026 |
| Israel DEB Chemical Group Co., Ltd | Mining & quarrying | 2026 |
| Israel Epoch Agricultural Chemical Co., Ltd | Mining & quarrying | 2026 |
| Israel Guopulifu Special Fertilizer Ltd | Mining & quarrying | 2021 |
| Israel Haifa Agricultural Chemical Co., Ltd | Extraterritorial | 2023 |
| Israel Haifa Group Chemical Industry Ltd | Extraterritorial | 2022 |
| Israel Haifa Mineral Chemical Co., Ltd. | Mining & quarrying | 2026 |
| Israel Haifa Ruinuo Chemical Co., Ltd | Mining & quarrying | 2026 |
| Israel Haifaer (UK) Co., Ltd | Mining & quarrying | 2026 |
| Israel Huanai Group Co., Ltd | Wholesale & retail | 2025 |
| Israel Migaodi International Chemical Co., Ltd | Wholesale & retail | 2022 |
| Israel Mineral Chemical Industry Group Limited | Extraterritorial | 2017 |
| Israel Norway International Holdings Co., Ltd | Extraterritorial | 2023 |
| Israel Ruent International Chemical Co., Ltd | Mining & quarrying | 2025 |
| Israel Runpute Biotechnology Co., Ltd | Wholesale & retail | 2023 |
| Israel Volcon (China) Chemical Group Co., Ltd | Manufacturing | 2021 |
| Israel Yafa Special Fertilizer Co., Ltd | Wholesale & retail | 2023 |
| Israel Zulon Liahull Mining Industry Co., Ltd | Wholesale & retail | 2023 |
| Ista Energy Solutions Limited | Information & communication | 1999 |
| Ista Metering UK Limited | Professional & scientific | 2004 |
| IT Auxilium Ltd | Information & communication | 2022 |
| IT CAN Happen Limited | Administrative & support | 2000 |
| IT Fore Ltd | Information & communication | 2011 |
| IT Support Partners Limited | Information & communication | 2004 |
| IT Takes a City (Cambridge) | Health & social care | 2019 |
| It's Good Goods Ltd | Wholesale & retail | 2020 |
| It's OUR Party Ltd | Wholesale & retail | 2023 |
| It@Work Consulting Limited | Information & communication | 2015 |
| Italian Jinweijin Crop Nutrition Technology Co., Ltd | Mining & quarrying | 2025 |