| H. & T. Builders Supplies Limited | | 1970 |
| H.F.Sheffield Limited | Wholesale & retail | 1956 |
| H.S.E. Lighting & Electrical Services Limited | Administrative & support | 2006 |
| Halcyon Herts Lettings Limited | Real estate | 2003 |
| Hammer & Chisel Ltd | Extraterritorial | 2015 |
| Hampden Securities Limited | Construction | 1987 |
| Handside Developments (Welwyn) Limited | | 1976 |
| Hanmere Polythene Limited | Manufacturing | 1966 |
| Harbour JIG and Tool Co.Limited | Manufacturing | 1963 |
| Harkness New Roses Limited | Agriculture & fishing | 1967 |
| Harp Shop Ltd | Wholesale & retail | 2022 |
| Harpenden Developments Limited | Construction | 2005 |
| Harris Sacker Associates Limited | Professional & scientific | 2007 |
| Harrisons Tree Service Limited | Agriculture & fishing | 2009 |
| Hawksford Consultancy Services Ltd | Information & communication | 2007 |
| Hawthorns Residents Association Limited | Hospitality | 1986 |
| Hayle Harbour Rentals Limited | Real estate | 2006 |
| Haywood & Bonnett (Consultancy Services) LLP | | 2007 |
| HAZ International Ltd | Construction | 1990 |
| HBG UK Pension Trustee Limited | Financial services | 1984 |
| Head & Short Property Limited | Real estate | 2006 |
| Head-On Technology Limited | | 1992 |
| Helprose Limited | Wholesale & retail | 1982 |
| Hendon Property Services Limited | Real estate | 2006 |
| Hermoss Limited | Real estate | 2006 |
| Hertfordshire Design & Supply Company Limited | Wholesale & retail | 1993 |
| Hertfordshire Homes (Welwyn) Limited | Wholesale & retail | 1988 |
| Herts Afro Centre Ltd | Wholesale & retail | 2021 |
| Herts Building and Electrical Limited | | 1985 |
| Herts Construction Limited | Wholesale & retail | 1991 |
| Hertsmere Citizens Advice Bureau | Information & communication | 1997 |
| Hertsmere Property Co. Limited | Real estate | 1979 |
| Hickswood Services Ltd | Professional & scientific | 2007 |
| HILAL68 Ltd | Hospitality | 2025 |
| Hilite Litho Company Limited | | 1975 |
| Hill View Farm Shop Limited | Wholesale & retail | 2007 |
| Hillsworth Associates Ltd | Real estate | 2001 |
| HIP2DUPLICATE Limited | Information & communication | 2005 |
| Hitchin Legal Consultancy Limited | Professional & scientific | 2020 |
| Hoddesdon Limited | Real estate | 2004 |
| Hogarth Investment Properties Limited | Real estate | 2004 |
| Holmes Consultants Limited | Information & communication | 1981 |
| Holmes Golf Limited | Other services | 1995 |
| Holmes Promotions Limited | Professional & scientific | 1999 |
| Homes and Herts Limited | Construction | 2008 |
| Homeside Limited | Professional & scientific | 1983 |
| Hopepeak Limited | | 1978 |
| Hospice of ST. Francis (Berkhamsted) Limited | Health & social care | 1980 |
| House of Hair ZL Ltd | Other services | 2023 |
| Howbury Street Freehold Limited | Real estate | 2007 |
| Hoxton Investments Limited | Real estate | 2010 |
| Hubert Cecil Photography Ltd | Arts & recreation | 2024 |
| Huis Clos Investments Ltd | Financial services | 1988 |
| Hunting Gate UK Fund Limited Partnership | | 1994 |
| HYM Development Ltd | Real estate | 2018 |
| I-Rooms Limited | Wholesale & retail | 2005 |
| I.D.Products Limited | Real estate | 1959 |
| IA Consultants Ltd | Arts & recreation | 2005 |
| IAK Investments Ltd | Real estate | 2018 |
| Ice-Pr Limited | Other services | 2001 |
| Ickleford Bury Estate Company Limited | Construction | 1962 |
| Ickleford Bury Management Limited | Households | 1980 |
| ICL Consultants LP | | 2002 |
| Icompare Solutions Limited | Information & communication | 2025 |
| Ideas for Change Limited | Professional & scientific | 2003 |
| IDH PP Limited | Real estate | 2022 |
| IK Regulatory Limited | Health & social care | 2015 |
| Image 2 Limited | Professional & scientific | 1984 |
| Indiacrest Limited | | 1983 |
| Indloom Limited | Manufacturing | 1988 |
| Ingrained Carpentry Ltd | Construction | 2006 |
| Innerset Securities Limited | Real estate | 1983 |
| Innovahealth Ltd | Professional & scientific | 2017 |
| Insight Education and Publishing Services Ltd | Information & communication | 2023 |
| Interactive People | | 1996 |
| Interbear Limited | | 1986 |
| Interior Dimensions Limited | | 1986 |
| Invision Residential Care Group Ltd | Health & social care | 2026 |
| ISO Consulting & Co | | 1998 |
| Isource Limited | Information & communication | 2004 |
| Istrategy Ltd. | Professional & scientific | 2004 |
| ITQ South West Limited | Information & communication | 2005 |
| Ivor Lewis (Securities) Limited | Financial services | 1971 |
| J Ferguson Construction Limited | Construction | 2003 |
| J L Dale Limited | Information & communication | 2004 |
| J. a. Clark & SON (Funerals) Limited | Other services | 1984 |
| J.A.Robarts and J.J.Harding Limited | Agriculture & fishing | 1931 |
| J2 Interiors Ltd | Transport & logistics | 2003 |
| Jackson-Green Limited | Real estate | 2004 |
| Jagdee Limited | Wholesale & retail | 2008 |
| Jahronic Ltd | Information & communication | 2008 |
| Jahtech Limited | Information & communication | 2018 |
| James Aero Limited | Education | 2003 |
| James Carol Books Limited | Other services | 2014 |
| Jbak Company Ltd | Information & communication | 2018 |
| JDP Services Ltd | Professional & scientific | 2019 |
| Jennery Limited | Hospitality | 1980 |
| Jenrix Ltd | Professional & scientific | 2011 |
| Jhargon Limited | Financial services | 2016 |
| JJG Scenery Ltd | Construction | 2024 |