| Hulme & Snowling Properties Limited | Real estate | 2013 |
| Humanum Limited | Professional & scientific | 2016 |
| Humberts Oxford Ltd | Real estate | 2022 |
| Humentum UK | Professional & scientific | 2000 |
| Humphreys Electrical Services Ltd | Construction | 2020 |
| Humphris (Oxford) Limited | Wholesale & retail | 1986 |
| Humphris Limited | Construction | 1943 |
| Hunt GAS & Heating Ltd | Administrative & support | 2015 |
| Hunter Brook Limited | Professional & scientific | 2011 |
| Hunter Mckenzie International Limited | Financial services | 2015 |
| Hunter, Thomas & Company Ltd | Professional & scientific | 2015 |
| Hunters Reach Management Limited | Households | 1987 |
| Huntertech Limited | Professional & scientific | 2013 |
| Hunts (Oxford) Trading Limited | Extraterritorial | 2017 |
| Hunts Mill (Flats Management) Limited | Households | 1984 |
| HUONG328 Ltd | Hospitality | 2024 |
| Hurst House (Oxford) Management Company Limited | Households | 2024 |
| Hussey Estates Hastings Limited | Real estate | 2014 |
| Hussey Estates Limited | Real estate | 2013 |
| Hutchinson Education Limited | Education | 2018 |
| Hutton Parker Property Management Limited | Administrative & support | 2009 |
| Hvmr Consulting Ltd | Professional & scientific | 2021 |
| HW Realty Co. Ltd | Financial services | 2023 |
| HWL Innovation Limited | Administrative & support | 1999 |
| Hwli Holdings Limited | Financial services | 2001 |
| HWR (Oxford) Limited | Construction | 2020 |
| HWS Business Claims Ltd | Professional & scientific | 2024 |
| Hyatt.Pa Ltd | Health & social care | 2018 |
| HYB Distribution Ltd | Wholesale & retail | 2026 |
| Hybont Limited | Energy | 2023 |
| Hybrid Memoirs Press Ltd | Information & communication | 2025 |
| Hybrint Ltd | Information & communication | 2024 |
| Hycap Limited | Administrative & support | 2021 |
| Hyderabad Eats Ltd | Wholesale & retail | 2025 |
| Hydrab Power Limited | Administrative & support | 2020 |
| Hydrab Power Nominees Limited | Administrative & support | 2024 |
| Hydrab Services Limited | Administrative & support | 2023 |
| Hydrogen Equity Partners UK Limited | Professional & scientific | 2020 |
| Hygen Ballymena Limited | Administrative & support | 2022 |
| Hygen Energy Holdings Limited | Financial services | 2022 |
| Hygen Energy Limited | Administrative & support | 2018 |
| Hygen Power Assets Limited | Administrative & support | 2022 |
| Hygen Power Energy Limited | Administrative & support | 2022 |
| Hygen Power Fuel Cells Limited | Administrative & support | 2022 |
| Hygen Power Systems Limited | Administrative & support | 2022 |
| Hygen Production Limited | Administrative & support | 2022 |
| Hygen Renewables Limited | Administrative & support | 2022 |
| Hynefield Properties Limited | Extraterritorial | 1993 |
| Hype Energy UK Ltd | Wholesale & retail | 2023 |
| Hyperbat Limited | Manufacturing | 2018 |
| Hyperion Live Limited | Information & communication | 2022 |
| Hyperion Management (London) Limited | Financial services | 2017 |
| Hyport LOW Carbon Hydrogen Limited | Administrative & support | 2022 |
| HZ Entertainment Limited | Arts & recreation | 2013 |
| I & D Dwellings Limited | Real estate | 2017 |
| I Love Supersport Ltd | Professional & scientific | 2023 |
| I Real Smart Store Ltd | Wholesale & retail | 2022 |
| I S Gill Consulting Ltd | Professional & scientific | 2016 |
| I-Po Depar Ltd | Hospitality | 2018 |
| I-Space Living Ltd | Real estate | 2020 |
| I-Transport Futures LLP | | 2024 |
| I-Transport LLP | | 2005 |
| IA Mangement Consulting Ltd | Professional & scientific | 2020 |
| IA25 Stem Ltd | Administrative & support | 2025 |
| IAN Bottrill Limited | Health & social care | 2015 |
| IAN Bridge Consultancy Limited | Professional & scientific | 2013 |
| IAN Goldin Limited | Administrative & support | 2009 |
| IAN Kench Ltd | Arts & recreation | 2018 |
| IAN Mcewan | Information & communication | 2010 |
| IAN Salisbury Limited | Professional & scientific | 2000 |
| IAT Education Limited | Education | 1987 |
| IAW Engineering and Manufacturing Services Limited | Professional & scientific | 2026 |
| Ibnsina Mindcrafters C.I.C. | Administrative & support | 2018 |
| Ibra Construction Ltd | Construction | 2018 |
| IC Estates Limited | Real estate | 2017 |
| IC Filling Systems Ltd | Wholesale & retail | 2015 |
| IC Health Solution Ltd | Wholesale & retail | 2025 |
| Ic-Vec Limited | Professional & scientific | 2001 |
| Icanware Business Solutions Limited | Information & communication | 2000 |
| ICC IP Limited | Professional & scientific | 2019 |
| Icfds Global Limited | Arts & recreation | 2013 |
| ICO Business Solutions Ltd | Transport & logistics | 2025 |
| Icon Hire Limited | Transport & logistics | 2016 |
| Iconic Frame Limited | Professional & scientific | 2024 |
| Iconic Gems Limited | Wholesale & retail | 2021 |
| Icosphere Biosciences Ltd | Professional & scientific | 2024 |
| Icreate Building Ltd | Construction | 2020 |
| Icsi Ltd | Other services | 2025 |
| ID3 Services Limited | Information & communication | 2017 |
| Ideal Eyes Limited | Health & social care | 1989 |
| Ideal Holidays Ltd | Administrative & support | 2023 |
| Idealogistix Ltd | Transport & logistics | 2012 |
| Ideaslist & Co Limited | Manufacturing | 2015 |
| Idflex Limited | Transport & logistics | 2025 |
| Idle.Taxi Limited | Transport & logistics | 2025 |
| Idotdoodle Limited | Wholesale & retail | 2023 |
| IF Oxford Ltd. | Professional & scientific | 2010 |
| Iffley Lock Hotel Limited | Hospitality | 2025 |
| Iffley Press Limited | Information & communication | 2012 |
| Iffley Technologies Limited | Information & communication | 2017 |