| Ipss (Scotland) Limited | Aberdeen | 2021 |
| IPT Global UK Limited | Aberdeen | 2025 |
| Iranian OIL Company (U.K.) Limited | London | 1971 |
| Iratos UK Ltd | Islington | 2020 |
| Irbis Energy Group Ltd | Tonbridge | 2023 |
| Ireland Huskarli Fertilizer Ltd | Cambridge | 2025 |
| Ireland Smurfitt Marine Share Co., Ltd | Cardiff | 2026 |
| Ireland Teoranta Halobios Co., Ltd | Cambridge | 2025 |
| Ires-Geo Technology (UK) Limited | Livingston | 2016 |
| Irish Salt Mining and Exploration Company Limited-The | Carrickfergus | 1965 |
| Irish Wheatgrass Juice Ltd | Newtownards | 2012 |
| Ironaxis Ltd | Bridgend | 2025 |
| Ironrock Africa Metals & Minerals Limited | London | 2025 |
| Irons Geophysical Consulting Limited | Oxfordshire | 2005 |
| Ironstone Holdings Limited | Middlesbrough | 2023 |
| IRV Consultancy Limited | Aberdeen | 2016 |
| Irvine Rothnie Ltd | Montrose | 2015 |
| Irwin Offshore Inspection Services Limited | Blackpool | 2019 |
| Irwins Quality Aggregates Limited | Dungannon | 2012 |
| ISA45 Energy & Investment Group UK Ltd | Purley | 2024 |
| Isaa Construction Ltd | Norwich | 2017 |
| Iscs Services Limited | Aberdare | 2015 |
| ISH London Trading & Tech Ltd | London | 2022 |
| Island Barn Aggregates Limited | Birmingham | 1980 |
| Island Chalk & Lime Limited | Godshill | 2017 |
| Island Drilling Ltd | Aberdeen | 2022 |
| Island GAS (Singleton) Limited | Lincoln | 1971 |
| Island GAS Limited | Lincoln | 2003 |
| Islander Limited | Isle Of Wight | 2017 |
| Isle of Luing Trading Company Limited | Oban | 2005 |
| ISOL8 Limited | Aberdeen | 2017 |
| Israe L Badrointernationalchemical Group Co., Ltd | London | 2025 |
| Israel Agrochemical Co., Ltd | Cardiff | 2022 |
| Israel Aviv Chemical Group Corporation. Ltd | Cambridge | 2026 |
| Israel Bafeite Chemical Group Co., Ltd. | Cardiff | 2025 |
| Israel Bailiou International Chemical Ltd | Cambridge | 2021 |
| Israel Baindt Chemical International Co., Ltd | Cambridge | 2026 |
| Israel Belim Crop Nutrition Ltd | Cambridge | 2020 |
| Israel Buddisi Chemical Group Co., Ltd | London | 2023 |
| Israel Caribbean International Chemical Co., Ltd | Cambridge | 2026 |
| Israel Corolla International Group Ltd | Cambridge | 2026 |
| Israel Crop Nutrition Research and Development Center Limited | Beckenham | 2023 |
| Israel DEB Chemical Group Co., Ltd | Cambridge | 2026 |
| Israel Demeter Chemical Group Ltd | Weston-Super-Mare | 2021 |
| Israel Eipuri Fine Chemical Group Ltd | Kington | 2020 |
| Israel Epoch Agricultural Chemical Co., Ltd | Cambridge | 2026 |
| Israel Farm Teacher Division Crop Nutrition Co., Ltd | Cardiff | 2021 |
| Israel Gairuite Biology Engineering Ltd | Cardiff | 2022 |
| Israel Gidro Chemical Group Co., Ltd | West Midlands | 2023 |
| Israel Guopulifu Special Fertilizer Ltd | Cambridge | 2021 |
| Israel Haifa Adom Zhongnong Chemical Group Co., Ltd | London | 2025 |
| Israel Haifa Agricultural Science and Technology Co., Ltd | West Midlands | 2023 |
| Israel Haifa Mairuide Crop Nutrition Co., Ltd | West Midlands, England, | 2023 |
| Israel Haifa Mineral Chemical Co., Ltd. | Cambridge | 2026 |
| Israel Haifa Pulante International Trade Group Ltd | Beckenham | 2021 |
| Israel Haifa Ruinuo Chemical Co., Ltd | Cambridge | 2026 |
| Israel Haifaer (UK) Co., Ltd | Cambridge | 2026 |
| Israel Lifress Bio-Tech Co., Ltd | Stafford | 2025 |
| Israel Liwell Chemical Co., Ltd | Kington | 2022 |
| Israel Moanlini Crop Nutrition Co., Ltd | Beckenham | 2023 |
| Israel Ruent International Chemical Co., Ltd | Cambridge | 2025 |
| Israel Smart International Group Co., Ltd | Wembley | 2025 |
| Israel Vicente Chemical Group Co., Ltd | Suffolk | 2025 |
| Istrat Ltd | Ilfracombe | 2018 |
| Italian Jinweijin Crop Nutrition Technology Co., Ltd | Cambridge | 2025 |
| Italian Merlandi International Co., Ltd | Coventry | 2025 |
| Italian Plantoo Marine Biotech Ltd | Cambridge | 2025 |
| Italian Relagro Specialty Fertilizer Co., Ltd | London | 2025 |
| Italy Agar Chemical Co. Ltd | Cambridge | 2025 |
| Italy Antym Chemical Ltd | Cambridge | 2024 |
| Italy Contik Horticultural Fertilizer Co., Ltd | Cardiff | 2026 |
| Italy Dashani Horticultural Fertilizer Company Co., Ltd | Cambridge | 2024 |
| Italy Galas Co., Ltd | Cardiff | 2026 |
| Italy Giels (Europe) Chemical Group Co., Ltd | Cambridge | 2024 |
| Italy Kendo Crop Nutrition S.P.A Ltd | Cambridge | 2022 |
| Italy Leyi Crop Nutrition Co., Ltd | Beckenham | 2024 |
| Italy Manzusa Chemical Group Co., Ltd | Cardiff | 2026 |
| Italy Mesbo Mining Co., Ltd | Cardiff | 2026 |
| Italy Oberfu Stock Co., Ltd | Cardiff | 2026 |
| Italy Roca Nutrition Science Co., Ltd | Cambridge | 2026 |
| Italy Romawotai International Chemical Group Co., Ltd | Cambridge | 2025 |
| Italy Roncott Co., Ltd | Hatfield | 2025 |
| Italy Talagro Chemical Co., Ltd | Cambridge | 2024 |
| Italy Tavagaro Co., Ltd | West Midlands, England | 2024 |
| Italy Tecnobells.Rl Co., Ltd | Cambridge | 2026 |
| Italy Tomei Agricultural Chemical Co., Ltd | Cardiff | 2026 |
| Italy Visti Plant Nutrition Co., Ltd | Cardiff | 2026 |
| Italy Woshka International Group Co., Ltd | London | 2025 |
| ITC Platinum Development Ltd | London | 2011 |
| Itdata Limited | Coventry | 2023 |
| Ithaca (NE) E&P Limited | Leeds | 1980 |
| Ithaca (NE) Ukcs Limited | Leeds | 1997 |
| Ithaca Alpha (N.I.) Limited | Belfast | 2009 |
| Ithaca Causeway Limited | Leeds | 2007 |
| Ithaca Dorset Limited | Leeds | 1973 |
| Ithaca EF Limited | Leeds | 1999 |
| Ithaca Energy (North Sea) PLC | Aberdeen | 2018 |
| Ithaca Energy (UK) Limited | Aberdeen | 2004 |
| Ithaca Energy Holdings (UK) Limited | Aberdeen | 2012 |
| Ithaca Epsilon Limited | Leeds | 2006 |