- Handyman Express - London
- Hantarex International Ltd - London
- Happie Group - London
- Happy Computers Ltd - London
- Happy Finish - London
- Harley Street Accountants - London
- Harley Street Speech Therapy - London
- Harline Education Services - London
- Harringay Removals - London
- Harris Balcombe - London
- Harris International Marketing - London
- Hart Security - London
- Hartnell Taylor Cook - London
- Haseltine Lake & Co. - London
- Hawes & Curtis - London
- Hawki - London
- Haych Digital - London
- Hayden Training - London
- Hay's Zmb - London
- Haysmacintyre - London
- HD Project Cost Management - London
- HeadChannel Ltd - London
- Headshot London Photography - London
- Health & Care - London
- Health And Care - London
- Heat Pump Source - London
- Hector's Haus - London
- Hedin Heaters - London
- Heighten Accountants - London
- Helifix - London
- Help 4 I T - London
- Henderson Biomedical Ltd - London
- Hendon Sign Co - London
- Henry Poole & Co. - London
- Henry Schein Dental - London
- Henson Security - London
- Herbatint - London
- Herman Miller - London
- HestaBit Ltd. - London
- Hexagon Metrology Ltd - London
- Heyne Tillett Steel - London
- HFL Marine International Ltd - London
- HGC Technologies UK - london
- Hi Resolution Production ltd - London
- Higginson Staircases Ltd - London
- High Society - London
- Highlander Ltd - London
- Highmark Welding Installation Co. Ltd - London
- Highview Power Storage - London
- Hilditch & Key - London
Companies 1751 to 1800
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