| Hydro Mill Group Limited | Energy | 2016 |
| Hydropos Offshore Limited | Mining & quarrying | 2018 |
| Hydrostar Europe Ltd | Professional & scientific | 2020 |
| Hydrosurv Unmanned Survey (UK) Ltd | Professional & scientific | 2011 |
| Hygiene Disposables Group Limited | Wholesale & retail | 2008 |
| Hylas Research Limited | Information & communication | 2024 |
| Hyner Property Ltd | Real estate | 2025 |
| Hyperdestiny Limited | Professional & scientific | 1999 |
| Hyphapro Limited | Professional & scientific | 2025 |
| Hyslop Financial Services Limited | Administrative & support | 2018 |
| Hyslop Property Lets Ltd | Real estate | 2023 |
| Hyson Fairs Limited | Arts & recreation | 1998 |
| Hyvvu Limited | Hospitality | 2026 |
| HYY Ltd | Other services | 2020 |
| I a G (SW) Ltd | Hospitality | 2025 |
| I SPY Technology Limited | Construction | 2009 |
| I-Civils Limited | Construction | 2012 |
| I-Pico Limited | Financial services | 2009 |
| I-Student Cleans Limited | Administrative & support | 2021 |
| I. J. & B Property Limited | Households | 2023 |
| I.D. Inspiring Development Invest Uzbekistan Limited | Financial services | 2021 |
| I.J. Cannings & SON Limited | Construction | 1985 |
| I.K.N.G. Investments Limited | Administrative & support | 2011 |
| IAG Event Consultancy Limited | Professional & scientific | 2018 |
| Iamh Ltd | Professional & scientific | 2024 |
| IAN Board Ltd | Construction | 2026 |
| IAN Chick Contracts (South West) Limited | Construction | 1997 |
| IAN Darling Architectural Design Limited | Construction | 2017 |
| IAN Gent Limited | Transport & logistics | 2004 |
| Iatro Limited | Information & communication | 2017 |
| IB Safety SW Limited | Public administration | 2024 |
| Iber EXE Developments Ltd | Construction | 2025 |
| Ibounce (Exeter) Limited | Arts & recreation | 2017 |
| IC Gillard Ltd | Professional & scientific | 2026 |
| Ican (SW) Limited | Construction | 2021 |
| Icarus Energy Ltd | Energy | 2022 |
| Ice and EV Autocare Ltd | Wholesale & retail | 2026 |
| Ice Reign Limited | Wholesale & retail | 2006 |
| Iceburg Limited | Other services | 2018 |
| Iclo Ltd | Manufacturing | 2022 |
| Icon Bidco Limited | Financial services | 2018 |
| Icon Body Repairs Ltd | Wholesale & retail | 2022 |
| Icon Topco Limited | Financial services | 2018 |
| Icon Vehicle Solutions Ltd | Manufacturing | 2024 |
| ICU Electro-Tech Ltd | Manufacturing | 2025 |
| IDE Holdings Ltd | Real estate | 2023 |
| Ideas - Creative Design Limited | Professional & scientific | 2008 |
| Ideas Training Ltd | Professional & scientific | 2015 |
| Ideas-Creative Solutions Ltd | Professional & scientific | 2012 |
| Ideaworks AI Ltd | Information & communication | 2025 |
| Identity Properties Limited | Real estate | 2025 |
| Identity Realization Limited | Professional & scientific | 2003 |
| Idoneus Consulting Ltd | Professional & scientific | 2020 |
| Iestate Ltd | Real estate | 2020 |
| Ieuan Jones Carpentry Ltd | Construction | 2025 |
| If...Media Limited | Information & communication | 2009 |
| IFA Choice Limited | Administrative & support | 2009 |
| Ifind Limited | Professional & scientific | 1998 |
| IFW14 Promotions Ltd | Arts & recreation | 2024 |
| IG Trade Limited | Wholesale & retail | 2017 |
| Igifted Ltd | Information & communication | 2024 |
| IGL Capital Limited | Construction | 2021 |
| Igloo Installations Ltd | Construction | 2023 |
| Ignis Praesidium Ltd | Public administration | 2024 |
| Ignite SW Ltd | Construction | 2023 |
| Ikhaya Investments Ltd | Real estate | 2018 |
| Iklr Limited | Information & communication | 2021 |
| Il-Solutions 2025 Limited | Health & social care | 2025 |
| Ilec Energy Ltd | Construction | 2022 |
| Ilec Group Limited | Construction | 2017 |
| Ilexalex Ltd | Agriculture & fishing | 2025 |
| Illumine Candle Co. Ltd | Manufacturing | 2020 |
| Iluvm Labs Ltd | Wholesale & retail | 2026 |
| IM Total Construction Ltd | Construction | 2021 |
| Image Display POS Limited | Manufacturing | 2011 |
| Image Tattoo & Piercing Ltd | Other services | 2026 |
| Imagine My Ltd | Information & communication | 2023 |
| Imani Thompson Limited | Information & communication | 2025 |
| Imbert Commercial Limited | Other services | 2019 |
| Imbert Limited | Real estate | 2006 |
| Imbert Square Limited | Other services | 2019 |
| IMC Tiling Limited | Construction | 2008 |
| IMMACULATE360 Limited | Manufacturing | 2025 |
| Immunity Festival Ltd | Arts & recreation | 2022 |
| IMP Software Bidco Limited | Financial services | 2025 |
| IMP Software Holdco Limited | Financial services | 2025 |
| IMP Software Ltd | Information & communication | 2019 |
| Impact Coaching International Ltd | Professional & scientific | 2024 |
| Impact Growth Marketing Ltd | Professional & scientific | 2016 |
| Impellor Limited | Construction | 2003 |
| Imperial Games Limited | Wholesale & retail | 2019 |
| Imperium Property Group Ltd | Real estate | 2015 |
| Impressions (Exeter) Limited | Real estate | 2004 |
| Improving Research Limited | Professional & scientific | 2012 |
| Imran Barbers Ltd | Other services | 2025 |
| IN 2 Publishing Limited | Information & communication | 2020 |
| IN Better Hands Homecare Ltd | Health & social care | 2025 |
| IN Car Technologies Limited | Wholesale & retail | 2000 |
| IN Control Recovery Ltd | Professional & scientific | 2012 |
| IN Production Music Publishing Ltd | Information & communication | 2015 |