| IOR Group Limited | Construction | 1989 |
| IOV Logistic Ltd | Transport & logistics | 2026 |
| IOW View Caravan Park Ltd | Construction | 2018 |
| IP Foods Ltd | Hospitality | 2023 |
| IP65 Limited | Professional & scientific | 2009 |
| Ipen Limited | Professional & scientific | 2025 |
| Ipiera Limited | Information & communication | 2005 |
| Iplocker! Limited | Information & communication | 2024 |
| Iqbal Lettings Ltd | Real estate | 2021 |
| Iqma Limited | Administrative & support | 2018 |
| Iqra Community Centre Southampton | Other services | 2010 |
| Iquo Enterprise Ltd | Wholesale & retail | 2026 |
| IRC Property Limited | Real estate | 2025 |
| Iride Ltd | Transport & logistics | 2024 |
| Iride New Forest Ltd | Transport & logistics | 2024 |
| Irina Fruit Ltd | Construction | 2025 |
| Iris & Cole Ltd. | Manufacturing | 2017 |
| Irish Cottages Estate Management Company Limited | Real estate | 2013 |
| Irish Ship Management UK Ltd | Transport & logistics | 2023 |
| IRO Transport Group (ITG) Limited | Transport & logistics | 2017 |
| Iron Edge Solutions Limited | Construction | 2025 |
| Ironclad Extraction Ltd | Construction | 2026 |
| Irongate Developments Ltd | Construction | 1998 |
| Irving Stores Limited | Wholesale & retail | 2021 |
| Irwin Contracting Services Ltd | Professional & scientific | 2020 |
| ISA Minibus Transfers Ltd | Transport & logistics | 2025 |
| ISA Payouts Limited | Administrative & support | 2024 |
| Isaacs Cafe Limited | Hospitality | 2014 |
| Isaacs Gelato Limited | Extraterritorial | 2015 |
| Isabel Johnston Communications Ltd | Professional & scientific | 2022 |
| Isabell Imaging Ltd | Health & social care | 2015 |
| Isan Home Ltd | Professional & scientific | 2023 |
| Isara Hub Ltd | Wholesale & retail | 2024 |
| Isca Global Trading Ltd | Wholesale & retail | 2019 |
| Ishan Stores Ltd | Wholesale & retail | 2025 |
| Ishine Cleaning Solutions Ltd | Administrative & support | 2025 |
| Isla Bay Bakery Ltd | Hospitality | 2023 |
| Island Juice Ltd | Hospitality | 2023 |
| Island Lodges Ltd | Professional & scientific | 2013 |
| Isle of Wight Breaks Ltd | Hospitality | 2019 |
| Isle of Wight Care Holdings Limited | Financial services | 2023 |
| Ismarine Ltd | Wholesale & retail | 2021 |
| Isnorkel Investments Ltd | Real estate | 2019 |
| ISODO3D Limited | Professional & scientific | 2013 |
| Ispourt Digital Service Ltd | Information & communication | 2024 |
| IST Group Limited | Professional & scientific | 2026 |
| Istafaproperties Ltd | Real estate | 2025 |
| IT Auto Repairs Limited | Wholesale & retail | 2019 |
| IT CAN BE Calibrated Limited | Manufacturing | 2014 |
| IT Custodian Ltd | Information & communication | 2024 |
| IT Innovation Centre Limited | Professional & scientific | 1991 |
| IT Innovation Limited | Professional & scientific | 1999 |
| IT Makes Sense Limited | Information & communication | 1994 |
| IT Regatta Limited | Arts & recreation | 2004 |
| IT Squad Global Ltd | Information & communication | 2020 |
| It's Clicked Ltd | Other services | 2004 |
| It-Dst Limited | Information & communication | 2018 |
| Itag-Will UK Ltd | Real estate | 2017 |
| Italia Navis Ltd | Professional & scientific | 2026 |
| Italian Boutique Ltd | Wholesale & retail | 2020 |
| Italiya Companies Ltd | Wholesale & retail | 2025 |
| Itbc International Ltd | Professional & scientific | 2023 |
| Itcandor Limited | Professional & scientific | 2009 |
| Itchen Abbas Business Centre Road Limited | Real estate | 2021 |
| Itchen Houseboat Management Company Limited(The) | Households | 1983 |
| Itchen Marine (Towage) Limited | Transport & logistics | 1981 |
| Itchen Stationers Limited | Wholesale & retail | 1977 |
| Itchen View Management Limited | Households | 2008 |
| Iteach Music Limited | Education | 2009 |
| Itech Logic Limited | Information & communication | 2008 |
| ITP Lighting Limited | Professional & scientific | 2009 |
| ITS & Cyber Services Ltd | Information & communication | 2025 |
| ITS Architecture Ltd | Professional & scientific | 2021 |
| ITS Rose Ltd | Wholesale & retail | 2025 |
| Itsoton Ltd | Wholesale & retail | 2022 |
| Ittmind Limited | Information & communication | 2022 |
| Iturbo Limited | Information & communication | 2023 |
| ITV Lettings Ltd | Real estate | 2020 |
| Itzy Bar and Restaurant Limited | Hospitality | 2026 |
| IVO Estate Ukeig | | 2015 |
| Ivona Spedition Ltd | Transport & logistics | 2015 |
| Ivory GUM (PVT) Limited | Health & social care | 2013 |
| IVY & Wild Ltd | Wholesale & retail | 2024 |
| IVY Brew Limited | Hospitality | 2026 |
| Ivybridge Moving & Storage Limited | Professional & scientific | 2010 |
| Ivywood Limited | Professional & scientific | 2024 |
| IW Logistics Limited | Transport & logistics | 2006 |
| Iwfs Europe Africa Limited | Other services | 2014 |
| IWI Associates Limited | Professional & scientific | 1996 |
| Iykyk Beauty Ltd | Wholesale & retail | 2022 |
| Iykykhr Limited | Administrative & support | 2023 |
| Izzonic Ltd | Wholesale & retail | 2018 |
| I_Budgie-Yachting Limited | Arts & recreation | 2006 |
| J & B PVT Ltd | Real estate | 2025 |
| J & J Engineering (Southampton) Limited | Manufacturing | 1997 |
| J & J Pipeworx Ltd | Construction | 2023 |
| J & J Shipping Limited | Transport & logistics | 2017 |
| J & L Finance Management Limited | Professional & scientific | 2002 |
| J & M Drainage Ltd | Transport & logistics | 2022 |
| J & N Perez Services Ltd | Real estate | 2025 |