| Harris Technical and Professional Services Limited | Professional & scientific | 2015 |
| Hart to Heart Limited | Professional & scientific | 2015 |
| Haynes Bros(Wallingford)Limited | Wholesale & retail | 1961 |
| Hazel Grove Management Limited | Administrative & support | 1998 |
| HB Licensing Limited | Administrative & support | 2006 |
| HDA Trustees Limited | Extraterritorial | 2020 |
| Head Carpentry Ltd | Construction | 2026 |
| Head South Limited | Other services | 2006 |
| Healthcare Research Group Ltd | Professional & scientific | 2005 |
| Healthcare Research Worldwide Limited | Information & communication | 2001 |
| Healthcheck Consulting Limited | Professional & scientific | 2025 |
| Heart Doctor Mark Limited | Health & social care | 2025 |
| Heather Emerson Limited | Professional & scientific | 2011 |
| Heather's Diner Limited | Hospitality | 2023 |
| Hedges Law Employee Ownership Trustee Limited | Professional & scientific | 2021 |
| Hedges Law Limited | Professional & scientific | 2010 |
| Heel 2 TOE Cobblers Limited | Other services | 2025 |
| Held Collective Ltd | Professional & scientific | 2024 |
| Helen Ashton Ltd | Arts & recreation | 2016 |
| Helen Webb Aviation Limited | Professional & scientific | 2022 |
| Helen Webb Marketing Limited | Professional & scientific | 2022 |
| Helen Whitworth Marketing Limited | Professional & scientific | 1998 |
| Helios Foundation for Supply Chain | Professional & scientific | 2009 |
| Hellenic Systems Ltd | Information & communication | 1988 |
| Helo Homes Ltd | Real estate | 2026 |
| Help I'Ve Broken IT Limited | Manufacturing | 2019 |
| Hemphill and Jones Ltd | Information & communication | 2022 |
| Henley 4X4 Ltd | Wholesale & retail | 2018 |
| Henley Events Hosting Ltd | Hospitality | 2015 |
| Hennox UK Ltd | Wholesale & retail | 2021 |
| Henwood Halcyon Limited | Manufacturing | 2002 |
| Herridge Pottery Ltd | Manufacturing | 2024 |
| Heycakey Ltd | Wholesale & retail | 2024 |
| Hflogs Ltd | Agriculture & fishing | 2017 |
| High Tide Trading Ltd | Information & communication | 2025 |
| Highshotphoto Limited | Professional & scientific | 2010 |
| Hildred Farms Limited | Agriculture & fishing | 1964 |
| Hint of Tints Limited | Other services | 2019 |
| Hive Keep Limited Partnership | | 2025 |
| Holcroft Property Consultants Ltd | Real estate | 2017 |
| Hollie Stillion Ltd | Professional & scientific | 2022 |
| Home Condition Survey Limited | Real estate | 2006 |
| Home Counties Refurbishments Limited | Construction | 2020 |
| Homebase Property Management Limited | Real estate | 2005 |
| Homes Direct Limited | Real estate | 2024 |
| Honey Lane Management (Cholsey) Limited | Real estate | 2024 |
| Hong Kong House Wallingford Ltd | Hospitality | 2023 |
| Horace William Ltd | Professional & scientific | 2021 |
| Hornet Systems Limited | Information & communication | 2008 |
| Horsebox Coffee Events Ltd | Hospitality | 2021 |
| Horsebox Coffee Holdings Ltd | Financial services | 2021 |
| Hospitality Tech Holdings Limited | Administrative & support | 2019 |
| Hot Wash UK Ltd | Extraterritorial | 2023 |
| Housing Consulting Ltd | Professional & scientific | 2023 |
| Howard Stewart Ltd | Real estate | 1984 |
| HPI Verification Services Ltd | Professional & scientific | 2010 |
| HR Outsourced Solutions Limited | Administrative & support | 2016 |
| HR Wallingford Coretecx Limited | Information & communication | 2023 |
| HS10 Enfield Limited | Other services | 2018 |
| HTS Creative Limited | Administrative & support | 2003 |
| HTS Group Holdings Limited | Administrative & support | 2025 |
| Hudson Hives Partnership Limited | Professional & scientific | 2000 |
| Hugh Jackson Limited | Information & communication | 2025 |
| Humanitas Meritus Limited | Other services | 2012 |
| Hush Craft Ltd | Manufacturing | 2015 |
| Hutch Consulting Ltd | Health & social care | 2008 |
| Hyacinth Property Ltd | Real estate | 2019 |
| Hybrid Learning Specialists Ltd | Education | 2020 |
| I.A.R Paving Ltd | Construction | 2021 |
| IAN C Goodrich Garden Contractors Limited | Administrative & support | 2025 |
| Ibex Search and Selection Limited | Administrative & support | 1998 |
| Ice Park Limited | Administrative & support | 2017 |
| Idaeus Limited | Professional & scientific | 2023 |
| Idle Complexities Ltd | Information & communication | 2012 |
| IDS Operations Ltd | Professional & scientific | 2006 |
| Idyllic Construction Ltd | Construction | 2023 |
| Ignatia Consulting Limited | Professional & scientific | 2000 |
| Illara Limited | Wholesale & retail | 2025 |
| Imaginet Limited | Information & communication | 1995 |
| Imedical Innovations Ltd | Information & communication | 2010 |
| Imedical Mobile Ltd | Information & communication | 2011 |
| Immer Limited | Professional & scientific | 2021 |
| Imogen Dental Limited | Health & social care | 2013 |
| Imperisoft Ltd | Information & communication | 2025 |
| Impulse Technology Limited | Professional & scientific | 2026 |
| IN House Estateagents Ltd | Real estate | 2007 |
| Incite Change Limited | Administrative & support | 2011 |
| Incite Environmental Ltd | Professional & scientific | 2024 |
| Incite Insight Ltd | Information & communication | 2024 |
| Inclusive Agent Ltd | Professional & scientific | 2022 |
| Inclusive Therapies Ltd | Health & social care | 2025 |
| Inframatic Engineering Limited | Professional & scientific | 2025 |
| Inframatic Limited | Professional & scientific | 2019 |
| Infuzi Ltd | Wholesale & retail | 2018 |
| Innovata Communications Limited | Professional & scientific | 2007 |
| Innovision Projects Ltd | Professional & scientific | 2016 |
| Inreach Housing Ltd | Hospitality | 2025 |
| Integra PM Ltd | Construction | 2020 |
| International Water Specialists Ltd | Professional & scientific | 2007 |
| Invisiblemanservices Limited | Other services | 2025 |