| Industrial Partners (Midlands) Limited | Other services | 2000 |
| Industrial Rubber Group Limited | Financial services | 2026 |
| Industrial Rubber Limited | Manufacturing | 1997 |
| Indwell Property Ltd | Professional & scientific | 2022 |
| Inertia Safety Limited | Administrative & support | 2014 |
| Infiinite Limited | Information & communication | 2018 |
| Infinigate Cloud UK Ltd | Information & communication | 2017 |
| Infinity Renewables Ltd | Other services | 2022 |
| Info-Files Computing Limited | Information & communication | 1997 |
| Infocus Locums Ltd | Professional & scientific | 2025 |
| Infosec People Limited | Administrative & support | 2007 |
| Infotect Limited | Construction | 2008 |
| Ingham Construction Services Limited | Construction | 2009 |
| Ingleside Holdings Limited | Financial services | 2025 |
| Ingsc Consulting Ltd | Professional & scientific | 2019 |
| INK Masters Holdings Ltd | Other services | 2026 |
| INL Electrical Contracting & Testing Ltd | Construction | 2011 |
| Inn Credit Limited | Financial services | 2004 |
| Innovaction Global Ltd | Professional & scientific | 2021 |
| Innovate 4 Limited | Professional & scientific | 2011 |
| Innovate Flooring Limited | Wholesale & retail | 2025 |
| Innovate G&E Ltd | Professional & scientific | 2026 |
| Innovate Holdings Limited | Manufacturing | 2018 |
| Innovate Signs Limited | Manufacturing | 2002 |
| Innovation Events & Design Ltd | Construction | 2018 |
| Innovation Group Business Services Limited | Administrative & support | 2016 |
| Innovation Group Holdings Limited | Financial services | 2019 |
| Innovation Hair & Beauty Ltd | Other services | 2015 |
| Innovation Mouldings Limited | Manufacturing | 2006 |
| Innovation Products Ltd | Wholesale & retail | 2014 |
| Innovation Property (UK) Limited | Other services | 1999 |
| Innovation Squad Ltd | Administrative & support | 2014 |
| Innovations in Primary Care Ltd | Health & social care | 2005 |
| Innovative Access and Evidence Limited | Professional & scientific | 2024 |
| Innovault Group Limited | Financial services | 2026 |
| Innovisual Digital Marketing Agency Ltd | Professional & scientific | 2021 |
| INOV8 Interiors Limited | Administrative & support | 2017 |
| Insensys Holdings Limited | Professional & scientific | 2006 |
| Insensys Limited | Professional & scientific | 1990 |
| Inside-Outside-Suffolk Travels Limited | Transport & logistics | 2025 |
| Insiders TCG Ltd | Wholesale & retail | 2025 |
| Insight Services Southern Limited | Construction | 1998 |
| Inspect 2 Pass Limited | Education | 2024 |
| Inspiration Lifestyle Services Limited | Real estate | 2008 |
| Inspired Systems Engineering Ltd | Professional & scientific | 2016 |
| Inspiring Active Pathways C.I.C. | Education | 2025 |
| Inspiring Minds Limited | Health & social care | 2018 |
| Instant Propulsion Labs Ltd. | Hospitality | 2025 |
| Institute of Construction Management Limited(The) | Other services | 1978 |
| Insured Life Limited | Financial services | 2025 |
| Intec Recruitment Services Limited | Administrative & support | 1985 |
| Integrate Accountants Limited | Professional & scientific | 2020 |
| Integrated Technical Solutions Group Limited | Financial services | 2019 |
| Integrity Plumb Limited | Construction | 2025 |
| Integrity Yacht Management Ltd | Professional & scientific | 2026 |
| Intelligence Mortgage Solutions Ltd | Financial services | 2013 |
| Intelligent Flow International Limited | Professional & scientific | 2026 |
| Intelligent Pool System Ltd | Construction | 2011 |
| Intelligent Property Systems Ltd | Construction | 2020 |
| Intelligentsa Limited | Professional & scientific | 2014 |
| Intelsya Limited | Professional & scientific | 2024 |
| Inter-Franc (Lodges) Limited | Construction | 2005 |
| Internal Environments Southern Limited | Energy | 2013 |
| Internal Facilities Limited | Energy | 2017 |
| Internal Solutions (Southern) Limited | Energy | 2019 |
| International Glazing Services Limited | Manufacturing | 2002 |
| International Growth Hub Limited | Professional & scientific | 2022 |
| International House Kingswood Limited | Construction | 2019 |
| International Maritime Employers Council Limited | Other services | 2004 |
| Interpro Software Development Limited | Information & communication | 2016 |
| Interpro Technology Solutions Limited | Other services | 2010 |
| Intra Legem Limited | Professional & scientific | 2015 |
| Inventory Outline Ltd | Professional & scientific | 2011 |
| Inverness Specsavers Hearcare Limited | Wholesale & retail | 2023 |
| Inverness Specsavers Limited | Wholesale & retail | 1999 |
| Inverness Visionplus Limited | Wholesale & retail | 1999 |
| Inverurie Specsavers Limited | Wholesale & retail | 2003 |
| Invest Direct South Limited | Professional & scientific | 2012 |
| Invitro Genetics Limited | Health & social care | 2015 |
| Inyanga Moon Limited | Administrative & support | 2018 |
| IP Cortex Limited | Manufacturing | 2002 |
| IP NRG Solutions Limited | Construction | 2010 |
| IP Office Limited | Information & communication | 2002 |
| IPH Building Services Limited | Extraterritorial | 2019 |
| Iprotectu Limited | Information & communication | 2018 |
| Ipso Facto Training Solutions Limited | Information & communication | 1998 |
| Ipswich Specsavers Hearcare Limited | Wholesale & retail | 2005 |
| Ipswich Specsavers Limited | Wholesale & retail | 1987 |
| Ipswich Visionplus Limited | Wholesale & retail | 1993 |
| Iquo Limited | Administrative & support | 1998 |
| Iris Holdco Limited | Information & communication | 2020 |
| Iris Master Holdco Limited | Information & communication | 2020 |
| Irj.Io Ltd | Information & communication | 2015 |
| Iron Gate Studios RTM Company Ltd | Households | 2025 |
| Ironeye Visuals Limited | Information & communication | 2024 |
| Irvine Specsavers Hearcare Limited | Wholesale & retail | 2022 |
| Irvine Specsavers Limited | Wholesale & retail | 1992 |
| Irvine Visionplus Limited | Wholesale & retail | 1992 |
| Is-Np Projects Limited | Professional & scientific | 2026 |
| Island Court (Lee-On-Solent) Residents Company Limited | Households | 2011 |