| Health and Safety Management Solutions Ltd | Administrative & support | 2013 |
| Heayes Design Ltd | Administrative & support | 2015 |
| HEH Walker Technical Services Limited | Arts & recreation | 2017 |
| Height of Safety Limited | Professional & scientific | 2021 |
| Hellfire BBQ Co. Limited | Hospitality | 2021 |
| Hello Friend Group Limited | Wholesale & retail | 2022 |
| Henry Taylor Farms Limited | Agriculture & fishing | 2025 |
| HER Land Ltd | Agriculture & fishing | 2024 |
| Hertfordshire Horologists Limited | Other services | 2001 |
| Herts Traffic Management Limited | Administrative & support | 1977 |
| Hest Homes Ltd | Real estate | 2021 |
| Hexagon Motorsport Ltd | Wholesale & retail | 2022 |
| High Regard Films Ltd | Information & communication | 2023 |
| Highfield Asset Management Limited | Professional & scientific | 2014 |
| Highland Gate Limited | Households | 1989 |
| Highly Unlikely Limited | Information & communication | 2015 |
| Highview Insights Ltd | Professional & scientific | 2019 |
| Hiruki Limited | Professional & scientific | 2020 |
| Hitchcox Cider Limited | Manufacturing | 2019 |
| HJE Building Services Limited | Construction | 2021 |
| HJK Properties Ltd | Real estate | 2024 |
| Holgan Limited | Real estate | 2016 |
| Holiston Media Limited | Information & communication | 2018 |
| Holland Street Studio Ltd | Professional & scientific | 2020 |
| Hollandgreen Interior Design Limited | Professional & scientific | 2019 |
| Hollandgreen Landscaping Limited | Professional & scientific | 2019 |
| Hollandgreen Limited | Professional & scientific | 2010 |
| Holmes Lomas Ltd | Professional & scientific | 2023 |
| Home Counties Chauffeur Co Limited | Professional & scientific | 2010 |
| Honey BEE Productions Ltd | Information & communication | 2026 |
| Hooper Consultants Limited | Administrative & support | 2015 |
| HOP in Pubs Limited | Hospitality | 2015 |
| Hordern Close Haddenham Management Limited | Real estate | 1997 |
| Horizon Rehabilitation Limited | Health & social care | 2019 |
| Hotflair Limited | Wholesale & retail | 2005 |
| HOX Therapeutics Limited | Health & social care | 2013 |
| HP and Sons Limited | Real estate | 2017 |
| HPL Insurance Services Limited | Financial services | 2006 |
| HPW Properties LLP | | 2016 |
| Hudson and Charlett Roofing Limited | Construction | 2023 |
| Human Agency Ltd | Professional & scientific | 2021 |
| Humphris (Oxford) Crash Repair Centre Limited | Wholesale & retail | 2016 |
| Hunt Residential Limited | Real estate | 2019 |
| HV Property Services Limited | Construction | 2007 |
| Hyderpcg Ltd | Construction | 2024 |
| Hydregen Limited | Manufacturing | 2020 |
| Hyperkit Limited | Administrative & support | 2000 |
| I & SP 1 Ltd | Real estate | 2026 |
| I4 Asset Management Ltd | Administrative & support | 2019 |
| IAN Lawrence Crack Limited | Extraterritorial | 2023 |
| Ibex Energy Limited | Professional & scientific | 2025 |
| Ibiblios Limited | Information & communication | 2011 |
| Icape UK Limited | Wholesale & retail | 2003 |
| ICN Consulting Ltd | Information & communication | 2014 |
| Icottage Group Ltd | Information & communication | 2018 |
| IDM Estate Management Limited | Real estate | 2025 |
| IFA BDN Limited | Financial services | 2016 |
| Ignium Consulting Limited | Professional & scientific | 2018 |
| Imago Group Limited | Financial services | 2026 |
| Imago Holdings Limited | Information & communication | 1992 |
| Imago Publishing Limited | Information & communication | 1980 |
| Imperial Homes Southern Limited | Construction | 2024 |
| Imyhome.Co.Uk Limited | Other services | 2015 |
| Incognate Limited | Professional & scientific | 2004 |
| Industrial Physics Product Integrity Limited | Professional & scientific | 1991 |
| Ingell Design Ltd | Professional & scientific | 2025 |
| Ingram Digital Limited | Professional & scientific | 2023 |
| Inkpath Limited | Information & communication | 2016 |
| Innodys Limited | Wholesale & retail | 1997 |
| Innovation Construction Services Limited | Construction | 2019 |
| Inscape Solutions Limited | Professional & scientific | 1999 |
| Inspire Dietetic Consultancy Ltd | Health & social care | 2010 |
| Inspired Health Care Services Ltd | Public administration | 2025 |
| Instromeda Limited | Manufacturing | 2024 |
| Instyle Chauffeur Services Limited | Transport & logistics | 2008 |
| Instyle Chauffeurs Limited | Professional & scientific | 2019 |
| Insurance & Mortgage Solutions Ltd | Financial services | 2019 |
| Insyte UK Limited | Professional & scientific | 2023 |
| Intank Holdings Limited | Wholesale & retail | 2012 |
| Intank Technologies Limited | Wholesale & retail | 2004 |
| Integrity Engineering O&G Ltd | Mining & quarrying | 2011 |
| Intelligent Investment Services Limited | Administrative & support | 1998 |
| Intensive Solutions Limited | Health & social care | 2016 |
| Interim Business Management Limited | Professional & scientific | 2000 |
| International Road Racing Ltd | Arts & recreation | 2021 |
| INTERPRETING4U Ltd | Professional & scientific | 2022 |
| Intertwingled Innovations Limited | Information & communication | 2023 |
| Invessed Limited | Information & communication | 2024 |
| Investahm Ltd | Real estate | 2020 |
| Invictus Construction Group (Oxon) Ltd | Construction | 2016 |
| Invictus Fitness Centre Limited | Arts & recreation | 2018 |
| Invisible Connections Ltd | Manufacturing | 2014 |
| IP Stone Ltd | Construction | 2015 |
| Irene Barat Limited | Administrative & support | 2021 |
| Ironbrand Holdings Ltd | Financial services | 2020 |
| Ironbrand Ltd | Manufacturing | 2020 |
| Iska Health Ltd | Health & social care | 2019 |
| Islander Protect Services Limited | Administrative & support | 2024 |
| Isset's Projects Limited | Professional & scientific | 2018 |
| Iuvantium Limited | Professional & scientific | 2022 |