| Hill Rise Associates RTE Limited | Households | 2005 |
| Hillcroft Cleaning Services Limited | Other services | 1992 |
| Hillgrade Limited | Real estate | 2002 |
| Hillingdon Aids Response Trust Limited | Health & social care | 1994 |
| Hillingdon Community Transport Limited | Transport & logistics | 1985 |
| Hillingdon Glass Company Limited | Construction | 1983 |
| Hillingdon Greenprint Limited | Manufacturing | 2004 |
| Hillpark Resources Limited | Hospitality | 2010 |
| Hillpoint Limited | Real estate | 2005 |
| Hillview Properties Limited | Real estate | 2006 |
| Hinds Ltd | Professional & scientific | 2002 |
| Hitch Mylius Limited | Manufacturing | 1978 |
| Hitech Comm Ltd | Information & communication | 2017 |
| HK Smiles Ltd | Health & social care | 2026 |
| HLA Pest Control Services Ltd | Health & social care | 2005 |
| HLM Property Services Ltd | Real estate | 2023 |
| HM Technologies Ltd | Information & communication | 1998 |
| HMO Market Limited | Hospitality | 2020 |
| HMV Properties Limited | Real estate | 2004 |
| HNK Management Services Limited | Professional & scientific | 1998 |
| Hobo Limited | Construction | 1986 |
| Hogoc UK Limited | Manufacturing | 2002 |
| Holdens Associates Ltd | Administrative & support | 2003 |
| Hole 19 Limited | Hospitality | 2005 |
| Holiday World Limited | Administrative & support | 1998 |
| Holland Park Autos Limited | Wholesale & retail | 1996 |
| Hollman Garages (1979) Limited | Construction | 1956 |
| Holly Cottage Mews (Hillingdon) Resident Management Company Limited | Households | 1996 |
| Holly Village Enterprises Limited | Information & communication | 2003 |
| Holme-Sumner Investment Company Limited(The) | Construction | 1960 |
| Holmesdale Meadow Ltd. | Real estate | 1994 |
| Holmstall Parade Limited | Other services | 1972 |
| Home Counties Mortgage Protection & Finance Limited | Financial services | 2012 |
| Home Counties Support Services Ltd | Hospitality | 2024 |
| Home County Professional Services Ltd | Real estate | 1968 |
| Home From Home Letting Services Limited | Real estate | 1989 |
| Home-Start Hillingdon Limited | Health & social care | 2002 |
| Homegains Enterprises Ltd | Real estate | 2017 |
| Homestead Paddock Ltd | Construction | 2003 |
| Homestead Residential Ltd | Administrative & support | 2004 |
| Honest Construction Limited | Construction | 2006 |
| Honeycity Limited | Wholesale & retail | 1992 |
| Honeypot Superstores Ltd | Wholesale & retail | 1997 |
| Honeysuckle Rose Ltd | Wholesale & retail | 2026 |
| Honnete Limited | Construction | 2007 |
| Hons Chef Ltd | Hospitality | 2022 |
| Horace Notice | | 1998 |
| Horizon Carpentry Limited | Construction | 2020 |
| Horizon Entertainment Cargo Ltd | Transport & logistics | 2000 |
| Horn of Africa Youth Association | Education | 2004 |
| Hosemen Limited | Professional & scientific | 2007 |
| Hot One (UK) Limited | | 1996 |
| Hounslow Community Transport Limited | Other services | 1984 |
| Hounslow Rental Ltd | Real estate | 1996 |
| Hounslow Tamil Fine Arts Limited | Arts & recreation | 2004 |
| House of Haria Limited | Wholesale & retail | 1997 |
| House of Meera Limited | Real estate | 2001 |
| House of Parvi Ltd | Manufacturing | 2025 |
| Howard & SON Limited | Wholesale & retail | 2007 |
| Howard Morgan Consulting Limited | Professional & scientific | 1999 |
| HP Consult Ltd | Professional & scientific | 2013 |
| HP House Limited | Professional & scientific | 2025 |
| Hridhi Consulting Ltd | Administrative & support | 2017 |
| HRN Enterprises Limited | Wholesale & retail | 1991 |
| Hszhu Limited | Real estate | 2021 |
| Hucclecote Fencing & Landscaping Ltd | Administrative & support | 2026 |
| Hugh O'Neill | | 1998 |
| Hulk Scaffolding Limited | Construction | 2024 |
| Hullaballoon Limited | Arts & recreation | 2002 |
| Hungry Food Global Ltd | Wholesale & retail | 2025 |
| Hungry Years Ltd | Administrative & support | 2009 |
| Hungry's Kitchen Ltd | Hospitality | 2026 |
| Hunny POT Limited | Wholesale & retail | 2003 |
| Hunt Kennards Limited | Transport & logistics | 2000 |
| Huse Fencing Contractors Ltd. | Construction | 1999 |
| Hussains Limited | Extraterritorial | 2007 |
| Hutt & Lobb Plastering Limited | Wholesale & retail | 1986 |
| HV Financial Planning Limited | Financial services | 2001 |
| Hytheway Limited | Extraterritorial | 1983 |
| I C C T Limited | Construction | 1997 |
| I T Dealer.Com Limited | Information & communication | 2000 |
| I. COM Solutions Limited | Wholesale & retail | 1999 |
| I.N Construct Ltd | Construction | 2019 |
| I.N.S. Air Conditioning Limited | Energy | 2007 |
| Ianoda Ltd | Professional & scientific | 2007 |
| Iconfern Limited | | 1985 |
| Iconic Detailing Ltd | Wholesale & retail | 2024 |
| Iconic Time London Ltd | Wholesale & retail | 2019 |
| ICT Consultancy Services Ltd | Information & communication | 2008 |
| Ideal Project Solutions Ltd | Professional & scientific | 1996 |
| Ideal Public Relations Limited | Administrative & support | 2006 |
| Idera Labs Ltd | Information & communication | 2020 |
| IDN International Limited | Extraterritorial | 2002 |
| IDN Limited | Information & communication | 1987 |
| Iepp Ltd | Education | 2010 |
| Ifinger Limited | Information & communication | 2000 |
| Ildan Limited | Administrative & support | 2006 |
| Ileys Restaurant Ltd | Hospitality | 2025 |
| Ilidio Transportes Ltd | Transport & logistics | 2013 |
| Illumination Ltd | Professional & scientific | 2001 |