| Hot Air Herts Ltd | Arts & recreation | 2021 |
| Houghton Property Holdings Limited | Real estate | 2025 |
| House Healthcare Limited | Health & social care | 2025 |
| House of Gainz Limited | Arts & recreation | 2023 |
| Howdale Bloodstock Ltd | Agriculture & fishing | 2009 |
| Howdale Energy Ventures Limited | Other services | 2019 |
| Howdale Estate Company Ltd | Real estate | 2009 |
| Howe Redevelopments Limited | Real estate | 2020 |
| HR Coleman Ltd | Health & social care | 2022 |
| HRB Roofing and Cladding Ltd | Construction | 2014 |
| HRH Valeting Limited | Administrative & support | 2023 |
| HSP Business Services Limited | Professional & scientific | 2006 |
| Hubworth Ltd | Information & communication | 2021 |
| Hudson HAY HR Limited | Professional & scientific | 2017 |
| Hudson Underwriting Services Limited | Financial services | 2009 |
| Hudson White Holdings Limited | Administrative & support | 2018 |
| Hudson White Services Limited | Water & waste | 2012 |
| Hudsys Ltd | Information & communication | 2026 |
| Huflec Limited | Professional & scientific | 2020 |
| Hum's Remit Limited | Financial services | 2011 |
| Human Evolved AI Limited | Professional & scientific | 2026 |
| Hunton Properties Limited | Real estate | 2026 |
| Hurst Accountancy Limited | Extraterritorial | 2019 |
| Hutchinson International Trade Limited | Professional & scientific | 2025 |
| Hutton (Ancaster) Limited | Professional & scientific | 2016 |
| HY Nightingale Ltd | Administrative & support | 2021 |
| Hydrofido Limited | Professional & scientific | 2022 |
| Hyperion Building Services Ltd | Construction | 2018 |
| Hypernova Films Ltd | Information & communication | 2020 |
| I&M Property Investment 2025 Ltd | Real estate | 2025 |
| I-Breeder Network Ltd | Information & communication | 2022 |
| I. G Grindal & Sons Limited | Agriculture & fishing | 1960 |
| I.Net Internet Services Limited | Information & communication | 1999 |
| IAJ Group Ltd | Transport & logistics | 2023 |
| IC Grantham Transport Limited | Transport & logistics | 2024 |
| Ice House Street (NO.1) Limited | Financial services | 2011 |
| Ice House Street UK Limited | Financial services | 2014 |
| Iceblink Studios Ltd | Professional & scientific | 2011 |
| Icon Logistics Transport Ltd | Transport & logistics | 2026 |
| Iconic Engineering Solutions Ltd | Professional & scientific | 2013 |
| ICP Capital 2 Limited | Financial services | 2025 |
| ICP Capital Limited | Financial services | 2005 |
| ICP General Partner Limited | Financial services | 1994 |
| ICP Group Holdings Limited | Financial services | 2023 |
| ICP Holdings Limited | Financial services | 2006 |
| ICP MZ Investments Limited | Financial services | 2023 |
| ID Homes Ltd | Real estate | 2022 |
| ID Stays Ltd | Hospitality | 2024 |
| Ideal Air Limited | Professional & scientific | 2008 |
| Ideazeit Limited | Professional & scientific | 2014 |
| IDF (Holdings) Limited | Financial services | 2005 |
| Igluu Group Ltd | Other services | 2023 |
| Igold Ltd | Professional & scientific | 2026 |
| Igor Buildings Limited | Construction | 2025 |
| Ikhlas Retail Ltd | Wholesale & retail | 2025 |
| Ilai Ltd | Hospitality | 2023 |
| Ilasp Limited | Information & communication | 2019 |
| Iliffe Projects Ltd | Construction | 2014 |
| Imagination Town Ltd | Extraterritorial | 2019 |
| IMC Catering Limited | Hospitality | 2017 |
| Impact Rooms Ltd | Professional & scientific | 2021 |
| IN Verrem Limited | Administrative & support | 2020 |
| Inara Group Limited | Financial services | 2020 |
| Inara Systems Limited | Administrative & support | 2014 |
| Inchmore Technology Ltd | Information & communication | 2014 |
| Indepen Limited | Professional & scientific | 2009 |
| Independent Living Group Ltd | Other services | 2017 |
| Indre Shop Limited | Wholesale & retail | 2016 |
| Ines Medics Limited | Other services | 2024 |
| Infinite Polymer Extrusion Ltd | Manufacturing | 2022 |
| Ingrid Dean Ltd | Financial services | 2022 |
| INM Limited | Administrative & support | 2015 |
| Inner Studios Limited | Administrative & support | 2023 |
| Innovate Freight Holdings Limited | Information & communication | 2023 |
| Innovate Freight Limited | Information & communication | 2020 |
| Innovatus Leadership Consulting Limited | Professional & scientific | 2018 |
| Inshala NO. 1 Limited | Financial services | 2014 |
| Insight-Ful NFP Limited | Professional & scientific | 2014 |
| Insinvest Ltd | Financial services | 2023 |
| Inspire Plus | Education | 2011 |
| Integrated Design Consultants Limited | Professional & scientific | 2015 |
| Integrated Plastic Manufacturing Limited | Other services | 2008 |
| Integrity Recruitment Services Limited | Administrative & support | 2017 |
| Intelligent Insights Ltd | Professional & scientific | 2024 |
| Intelligent Structural Solutions Limited | Professional & scientific | 2011 |
| International Aardvark Limited | Professional & scientific | 2024 |
| International Rigspares Ltd | Professional & scientific | 2024 |
| Intsilo Limited | Information & communication | 2020 |
| Invest Grantham Ltd | Real estate | 2024 |
| Invest Surveying Ltd | Professional & scientific | 2026 |
| IPE Group Ltd | Wholesale & retail | 2022 |
| IPE Property Management Ltd | Real estate | 2023 |
| IPS Property Management Ltd | Real estate | 2022 |
| IQD Project Management Ltd | Professional & scientific | 2016 |
| Ireland Prods. Limited | Agriculture & fishing | 2022 |
| Iris Rayne Studios Ltd | Arts & recreation | 2024 |
| IRL Building and Renovation Ltd | Construction | 2023 |
| Irnham Events Limited | Arts & recreation | 2012 |
| IRS Consult Ltd | Professional & scientific | 2019 |
| Iscad Limited | Professional & scientific | 2016 |