| Hargrace Property Group Limited | Real estate | 2025 |
| Hargreaves Hatfield Limited | Financial services | 2018 |
| Hari Katha Sevak Sangh Limited | Other services | 2026 |
| Hari OM Legacy Ltd | Wholesale & retail | 2026 |
| Hari Property Limited | Real estate | 2022 |
| Harikrishna Beverages Ltd | Hospitality | 2017 |
| Harini Decorators Ltd | Construction | 2025 |
| Harini Investments Ltd | Real estate | 2021 |
| Hariprabodham Limited | Real estate | 2020 |
| Hariprro Ltd | Professional & scientific | 2021 |
| Haris Nukem Ltd | Professional & scientific | 2015 |
| Harisma Communications Limited | Information & communication | 2021 |
| Harium Ltd | Manufacturing | 2017 |
| Harki International Ltd | Professional & scientific | 2018 |
| Harlequin Theatricals Ltd | Arts & recreation | 2021 |
| Harley Mental Care Ltd | Health & social care | 2024 |
| Harley Plastering Ltd | Construction | 2026 |
| Harlin Homes Limited | Real estate | 2026 |
| Harlock Ltd | Information & communication | 2019 |
| Harmer Hyde Investments Limited | Construction | 1993 |
| Harmony Montessori Nursery Limited | Education | 2004 |
| Harmony Neuropsychology Clinic Limited | Education | 2025 |
| Harnel Group Ltd | Other services | 2016 |
| Harp Windows (Watford) Limited | Construction | 1989 |
| Harper Wealth Consulting Ltd | Professional & scientific | 2019 |
| Harri Properties Limited | Real estate | 2016 |
| Harris Calnan Holdings Limited | Professional & scientific | 2003 |
| Harris Film Services Ltd | Information & communication | 2020 |
| Harris Quality Halal Meat Ltd | Wholesale & retail | 2018 |
| Harrison Wallace Consulting Ltd | Professional & scientific | 2008 |
| Harrison Webb Media Ltd | Arts & recreation | 2025 |
| Harrisons Group Holdings Ltd | Financial services | 2026 |
| Harrisons Private Client Solutions Ltd | Administrative & support | 2011 |
| Harrisons Property Solutions Ltd | Real estate | 2021 |
| Harrow Audio Limited | Wholesale & retail | 2007 |
| Harrow Hotel Services Limited | Hospitality | 2008 |
| Harrow Ltd | Construction | 2024 |
| Harrow Optical Services Limited | Health & social care | 2002 |
| Harrow Physiotherapy Clinic Ltd | Health & social care | 2014 |
| Harry Charles Limited | Real estate | 2006 |
| Harshcg Ltd | Arts & recreation | 2018 |
| Harshon Real Estates Ltd | Real estate | 2012 |
| Harsiddhi Investments Ltd | Real estate | 2025 |
| Hart Homes (Watford) Development LLP | | 2017 |
| Hart Homes (Watford) Limited | Hospitality | 2016 |
| Hartnoll Limited | Other services | 1981 |
| Hartsbourne Ltd | Wholesale & retail | 2025 |
| Harvest Care Group Ltd | Administrative & support | 2010 |
| Harvest Case Management Ltd | Health & social care | 2024 |
| Harvest Harmony Ltd | Wholesale & retail | 2025 |
| Harvestmead Limited | Construction | 1984 |
| Harvey&Brown Property Services Ltd | Construction | 2024 |
| Harwood Cost Consultants Ltd | Professional & scientific | 2019 |
| Hary Ltd | Information & communication | 2012 |
| Hashroo Dynamic Consulting Ltd | Information & communication | 2019 |
| Hashtag the WRD Limited | Administrative & support | 2019 |
| Hashtags ETC Ltd | Information & communication | 2014 |
| Hasincop Ltd | Wholesale & retail | 2024 |
| Hasini Fine Seafood Trading Ltd | Wholesale & retail | 2026 |
| Haskapa Limited | Manufacturing | 2019 |
| Haslemere Collections Ltd | Wholesale & retail | 2013 |
| Hasselblad (UK) Limited | Wholesale & retail | 1985 |
| Hassnain Limited | Wholesale & retail | 2025 |
| Hatas Technology Leadership Ltd | Administrative & support | 2025 |
| Hatchcraft Limited | Professional & scientific | 2025 |
| Hatfield Road Management Company Limited | Households | 2011 |
| Hatfits Limited | Professional & scientific | 2013 |
| Hattie's Here Ltd | Other services | 2021 |
| Haul UK International Ltd | Wholesale & retail | 2023 |
| Haulage Distribution Ltd | Transport & logistics | 2024 |
| Haute Commerce Limited | Information & communication | 2015 |
| Have Limited | Professional & scientific | 2011 |
| Havelin Consultancy Ltd | Professional & scientific | 2016 |
| Haven HQ Ltd | Arts & recreation | 2026 |
| Havenbridge Housing CIC | Hospitality | 2025 |
| Hawberry Systems Limited | Information & communication | 2015 |
| Hawk-Fire Ltd | Construction | 2011 |
| Hawkley Rehab Ltd | Health & social care | 2019 |
| Hawthorn Flynn Ltd | Information & communication | 2019 |
| Hawthorn Housing Limited | Real estate | 2024 |
| Haxo Labs Ltd | Information & communication | 2024 |
| Haxton Solutions Ltd | Information & communication | 2011 |
| Haych Luxury Travel Ltd | Transport & logistics | 2024 |
| Hayer Consultancy Ltd | Professional & scientific | 2023 |
| Hayespdl Ltd | Education | 2025 |
| Haygreen Limited | Financial services | 2023 |
| Haylo Property Solutions Limited | Real estate | 2026 |
| Hayo Limited | Health & social care | 2014 |
| Hayward Gold Ltd | Construction | 2023 |
| Hayway Properties Ltd | Real estate | 2020 |
| Hayyat Consultants Ltd | Professional & scientific | 2022 |
| HAZ Afro Cosmetics Limited | Administrative & support | 2006 |
| HAZ Homes Ltd | Real estate | 2025 |
| Hazel Hospitality Ltd | Hospitality | 2021 |
| Hazelcraft Limited | Construction | 2026 |
| Hazlewood Park (Block 2) RTM Limited | Households | 2007 |
| HB Cater Supply Ltd | Wholesale & retail | 2020 |
| HBW Solutions Ltd | Information & communication | 2023 |
| HC Networks Ltd | Administrative & support | 2020 |
| Hccc Limited | Construction | 2012 |