| Hillside Radlett Freehold Ltd | Extraterritorial | 2025 |
| HJN Ltd | Households | 2022 |
| Hlfg Holdings Limited | Financial services | 2025 |
| Hodford Twenty-One RTM Company Limited | Other services | 2013 |
| Holden Heights Limited | Professional & scientific | 2009 |
| Holy Rebel Limited | Wholesale & retail | 2014 |
| Home Pilates Ltd | Arts & recreation | 2026 |
| Honey Airport Transfers Limited | Transport & logistics | 2026 |
| Hostbray Limited | Construction | 2021 |
| House of Antigone Limited | Information & communication | 2017 |
| Howard Place Residents Association (NO.1) Limited | Households | 1992 |
| Howard Place Residents Association (NO.2) Limited | Administrative & support | 1992 |
| Howe Street Capital Limited | Professional & scientific | 2020 |
| HRB Electrical Services Limited | Construction | 2022 |
| HRB Equestrian Ltd | Agriculture & fishing | 2025 |
| HRH Luxury Travel Limited | Transport & logistics | 2025 |
| Hudson DE Maeijer LLP | | 2010 |
| Hummingbird Motors (Borehamwood) Limited | Wholesale & retail | 2018 |
| Hyling Ltd | Professional & scientific | 2019 |
| Hypermind UK Ltd | Information & communication | 2017 |
| I&A Analytics Limited | Professional & scientific | 2012 |
| I'M SO Lucky Limited | Wholesale & retail | 2025 |
| I.E.A Tutoring Centre Ltd. | Education | 2014 |
| IAM Haven Properties Ltd | Real estate | 2026 |
| IAM Insight Consulting Ltd | Professional & scientific | 2025 |
| Ibarr Ltd | Construction | 2021 |
| Ibhb Ltd | Professional & scientific | 2023 |
| Ibmetrix Ltd | Professional & scientific | 2020 |
| Ideas in a Bubble Limited | Administrative & support | 2013 |
| Identifyaojm Limited | Professional & scientific | 2025 |
| Igtcs Ltd | Information & communication | 2025 |
| IL Carciofo Ltd | Hospitality | 2022 |
| Imed Pro Limited | Health & social care | 2025 |
| Imedco Limited | Construction | 1998 |
| Imnt Ltd | Administrative & support | 2024 |
| Ingeni IT Services Limited | Professional & scientific | 2014 |
| Innovative Health Consultancy Limited | Health & social care | 2007 |
| Innovative-Q Gifts Ltd | Manufacturing | 2022 |
| Inovai Group Ltd | Information & communication | 2025 |
| Inreal Group Ltd | Real estate | 2022 |
| Insight Technologies Limited | Administrative & support | 2015 |
| Integrated Surveys Limited | Professional & scientific | 1997 |
| Interchange Plus Ltd | Professional & scientific | 2000 |
| International Consulting Group PPP Ltd | Information & communication | 2021 |
| International Society for Krishna Consciousness Limited | Other services | 1969 |
| International Trade Corporation Limited | Wholesale & retail | 1991 |
| Intevia BIO Limited | Professional & scientific | 2026 |
| Investment Planner Ltd | Financial services | 2008 |
| Ironclad Ventures Ltd | Real estate | 2025 |
| Ironclad Wealth Ltd | Professional & scientific | 2024 |
| Isoimages UAV Ltd | Professional & scientific | 2020 |
| Isot Mediterranean Restaurant Ltd | Hospitality | 2023 |
| Iste Editions Limited | Information & communication | 1999 |
| Iste Limited | Manufacturing | 2003 |
| Iste Openscience Limited | Information & communication | 2015 |
| Iste Press Limited | Information & communication | 2001 |
| Iste Science Publishing Ltd | Manufacturing | 2003 |
| Iste Sciences Encyclopedia Ltd | Information & communication | 2018 |
| IT & AI Solutionz Limited | Information & communication | 2024 |
| Itemize Limited | Administrative & support | 2010 |
| Iwmm Ltd | Professional & scientific | 2020 |
| J S Hunter & Sons Ltd | Agriculture & fishing | 2011 |
| J W Bathrooms Limited | Wholesale & retail | 2018 |
| J&J Suterwalla Limited | Financial services | 2019 |
| J. E. Joseph Trustee Company Limited | Other services | 2018 |
| J.A. Corney Limited | Wholesale & retail | 1980 |
| J.A.R. Accountancy Limited | Professional & scientific | 2000 |
| J.Kaneria Ltd | Administrative & support | 2024 |
| J.R.F Properties 2 Ltd | Real estate | 2016 |
| J.R.F. Properties Limited | Other services | 2013 |
| Jaag Properties Ltd | Real estate | 2019 |
| Jacakoy Limited | Administrative & support | 2023 |
| JAM 7 Limited | Information & communication | 2023 |
| James G FX Limited | Information & communication | 2019 |
| Jandr Legal Services Limited | Professional & scientific | 2014 |
| Jasmine Bliss Nutrition Limited | Health & social care | 2023 |
| Jay's Delicatessen Ltd | Hospitality | 2011 |
| Jay's Restaurant Limited | Administrative & support | 2017 |
| Jazz Property Investments Limited | Real estate | 2021 |
| Jazz Services Limited | Professional & scientific | 2018 |
| JDM Investments Limited | Real estate | 2002 |
| Jemstone Financial Limited | Financial services | 1997 |
| Jemstone Income Limited | Financial services | 2012 |
| JEN (New Homes) Limited | Real estate | 2025 |
| Jennifer's Nails Radlett Ltd | Other services | 2025 |
| Jensco (Bold Lane) Limited | Construction | 2018 |
| Jensco (Brighton) Limited | Real estate | 2024 |
| Jensco (Broadnook 1) Limited | Real estate | 2025 |
| Jensco (Broadnook 2) Limited | Real estate | 2025 |
| Jensco (Derby) Limited | Construction | 2015 |
| Jensco (Great Haddon) Limited | Real estate | 2025 |
| Jensco (Hamilton House) Limited | Real estate | 2026 |
| Jensco (Longmoor) Limited | Real estate | 2025 |
| Jensco (New Homes) Limited | Real estate | 2025 |
| Jensco (Nottingham) Limited | Construction | 2019 |
| Jensco (Traffic Street) Limited | Real estate | 2019 |
| Jensco (Wilford Road) Limited | Construction | 2020 |
| Jensco Asset Management Limited | Real estate | 2025 |
| Jensco Direct Limited | Other services | 2002 |
| Jensco Holdings Limited | Financial services | 2016 |