| Hatfield District Centre Estate Management Company Ltd | Real estate | 2005 |
| Hawaiian Blue Limited | Information & communication | 2002 |
| Herts & Essex Fertility Centre Limited | Health & social care | 2007 |
| Herts & Essex Investments Limited | Real estate | 2017 |
| Herts Motors Van Sales Limited | Wholesale & retail | 2022 |
| High Efficiency Heating London Ltd | Construction | 2015 |
| Highbourne Investments Ltd | Real estate | 2014 |
| Hill Newton Recruitment Limited | Administrative & support | 2002 |
| Hilton Care Limited | Health & social care | 2002 |
| Hilton Community Services Limited | Health & social care | 2000 |
| Hilton Homes UK Investments Ltd | Financial services | 2020 |
| Hitec Laser Limited | Manufacturing | 1995 |
| Hitec Sheet Metal Ltd. | Manufacturing | 1992 |
| HJK Services Limited | Administrative & support | 2026 |
| Holtwhites Hill (Enfield) Management Company Limited | Households | 2001 |
| Home Entertainment Direct Ltd. | Wholesale & retail | 2007 |
| Hope Hall Stud Limited | Agriculture & fishing | 2013 |
| Howarth Armsby Ltd | Administrative & support | 2020 |
| Howarth Armsby Payroll Limited | Administrative & support | 2021 |
| HPD London Limited | Other services | 2013 |
| Hudsons Brake and Tyre Service Limited | Wholesale & retail | 1975 |
| HUM TUM Ltd | Professional & scientific | 2015 |
| Hummel UK Limited | Wholesale & retail | 2006 |
| Hunter Knights Ltd | Administrative & support | 2016 |
| Hydro GAS Group Ltd | Construction | 2023 |
| Hydro GAS Herts Ltd | Construction | 2021 |
| Hydro GAS Plumbing Ltd | Construction | 2023 |
| I R Projects Limited | Professional & scientific | 2015 |
| IAM Holdings Limited | Real estate | 2020 |
| IAN Gibbs (Broadfield Court) Limited | Households | 2001 |
| IAN Gibbs Estate Agents Limited | Real estate | 2009 |
| IAN Gibbs Properties Limited | Real estate | 2015 |
| Ice Cool Environments Ltd | Construction | 2003 |
| Ice Rocks Limited | Arts & recreation | 2007 |
| Ideonate Ltd | Professional & scientific | 2019 |
| IGN Consulting Structural Engineers Ltd | Construction | 2021 |
| Iheat Systems Limited | Construction | 2014 |
| Impermanence (UK) Limited | Other services | 2011 |
| Inchief Media Limited | Administrative & support | 2024 |
| Indalo Plant Limited | Administrative & support | 2000 |
| Independent Marketing Solutions Limited | Professional & scientific | 2021 |
| Infinite Gym Ltd | Health & social care | 2025 |
| Infranetix Ltd | Information & communication | 2025 |
| Ingleheart Picture Framing Limited | Manufacturing | 2013 |
| Innotrade Europe Limited | Financial services | 2013 |
| Innotrade Limited | Administrative & support | 2009 |
| Innotrend Limited | Manufacturing | 2018 |
| Innovate Productions Limited | Extraterritorial | 2010 |
| Inspire Retail Ltd | Wholesale & retail | 2024 |
| IP Fire Protection Ltd | Public administration | 2011 |
| IPH Consulting Limited | Professional & scientific | 2014 |
| Isaac Jordan Limited | Administrative & support | 2008 |
| Island Creative Limited | Professional & scientific | 1997 |
| Island Marketing Limited | Professional & scientific | 1988 |
| J & N Properties Limited | Real estate | 2009 |
| J Greenaway & Co Limited | Wholesale & retail | 1981 |
| J Lyons Builders Ltd | Extraterritorial | 2020 |
| J&B Brickwork Ltd | Construction | 2020 |
| J.A.B. Hire Services Limited | Construction | 1986 |
| J.Waters Ltd | Wholesale & retail | 2024 |
| J3 Partners Limited | Administrative & support | 2012 |
| JAG Singh Properties Limited | Real estate | 2026 |
| Jaggers, Sharpe and Dixon Limited | Construction | 1973 |
| JAY Import & Export Ltd | Wholesale & retail | 2026 |
| Jaymax Consult Limited | Professional & scientific | 2019 |
| JCR Security Services Limited | Administrative & support | 2023 |
| JDC GAS Services Limited | Construction | 2019 |
| Jemz Cake Box Ltd | Hospitality | 2011 |
| JFT Holdings Ltd | Administrative & support | 2017 |
| JGJ Investments Limited | Real estate | 2016 |
| JHD Contractors Limited | Construction | 2018 |
| JM3 Ltd | Real estate | 2016 |
| JMI Services London Ltd | Construction | 2011 |
| Joabi Travel Services Limited | Administrative & support | 2019 |
| JOE Morris Legacy Ltd | Information & communication | 2019 |
| Joe's Boxing Academy | Professional & scientific | 2025 |
| Johns & Kelynack (1998) Limited | Financial services | 1998 |
| Johnson Ross Tackle Limited | Wholesale & retail | 2002 |
| Jolly POS Limited | Information & communication | 2020 |
| Jonathan Hunt Lettings Limited | Real estate | 2007 |
| JPL Motors Ltd | Wholesale & retail | 2023 |
| JPM Homelets Ltd | Construction | 2018 |
| JPM Plant Hire Limited | Administrative & support | 2006 |
| JR Paint Services Ltd | Manufacturing | 2014 |
| JS Mataj Construction Ltd | Construction | 2017 |
| Just Bikes UK Limited | Transport & logistics | 2004 |
| K & J Panels Kent Ltd | Manufacturing | 2024 |
| K 2 (Holdings) Limited | Real estate | 2000 |
| K 2 Properties Limited | Real estate | 2000 |
| K&W Motor Imports Ltd | Wholesale & retail | 2025 |
| Kalaman Limited | Professional & scientific | 2012 |
| Keates Developments Limited | Real estate | 2009 |
| Kerriene Limited | Real estate | 1993 |
| Kevin Batchelor Consulting Ltd | Professional & scientific | 2016 |
| Kingdom Engineering Ltd | Construction | 2015 |
| Kings Country Property Division LLP | | 2010 |
| Kings First AID Training Ltd. | Education | 2016 |
| Kings Franchising LLP | | 2007 |
| Kings Group Limited Liability Partnership | | 2003 |
| Kings Lettings Agents LLP | | 2008 |