| Harmony Properties & HR Solutions Ltd | Real estate | 2025 |
| Harper Building and Maintenance Ltd | Construction | 2024 |
| Harpers Construction & Groundworks Limited | Construction | 2015 |
| Harpy Automotive Ltd | Wholesale & retail | 2025 |
| Harrison CM Ltd | Financial services | 2022 |
| Harrison Lightning Protection & Earthing Limited | Administrative & support | 2001 |
| Harrison Lightning Protection Limited | Administrative & support | 2013 |
| Harrisonhix Architecture and Surveyors Ltd | Professional & scientific | 2017 |
| Harriwell Ltd | Financial services | 2025 |
| Harrogate Developments Ltd | Construction | 2018 |
| Harrowgate Hill Heating & Property Maintenance Ltd | Construction | 2015 |
| Harrowgate Hill Lettings Limited | Real estate | 2025 |
| Harry Stablers MOT Centre Ltd | Wholesale & retail | 2015 |
| Harry’S Smash Burger Joint Ltd | Hospitality | 2026 |
| Hartburn Darlington Limited | Other services | 2021 |
| Hartburn Lofts and Extensions Ltd | Construction | 2016 |
| Hartley's Nurseries & Landscaping Ltd | Administrative & support | 2019 |
| Harvey & Hugo Limited | Professional & scientific | 2009 |
| Harvey Electrical Services (Northern) Limited | Construction | 2012 |
| Harvey Investments International Limited | Real estate | 2024 |
| Harvey Joinery Services (Northern) Limited | Construction | 2026 |
| Harveys (Houndgate) Ltd | Hospitality | 2018 |
| Hasan Omran Ltd | Health & social care | 2011 |
| Hasina (Darlington) Limited | Hospitality | 2017 |
| Hatch Luncheonette Limited | Hospitality | 2018 |
| Hatdarlington Ltd | Hospitality | 2025 |
| Hatyurn Ltd | Wholesale & retail | 2025 |
| Haughton Glazing Systems Ltd | Construction | 2022 |
| Haughton Green Motor Co Limited | Wholesale & retail | 2022 |
| Haughton Napoli Pizza Ltd | Hospitality | 2025 |
| Haus DER Bratwurste 2025 Ltd | Hospitality | 2025 |
| Haus of Aesthetics by Lizzie Limited | Health & social care | 2026 |
| Haus of Moss Ltd | Wholesale & retail | 2023 |
| Haux Holdings Limited | Hospitality | 2024 |
| Hauxwell Construction Services Ltd | Construction | 2019 |
| Haven and Hall Cleaning Ltd | Administrative & support | 2025 |
| Haven Properties 2017 Limited | Real estate | 2017 |
| Haven Showers Limited | Manufacturing | 2005 |
| Hayden Naylor Limited | Construction | 2023 |
| HB Fabrications Ltd | Manufacturing | 2026 |
| HBN Heated by Nature Limited | Construction | 2010 |
| HC Vocal and Performance Academy Limited | Arts & recreation | 2023 |
| Hc-One NO.6 Limited | Administrative & support | 2006 |
| HCB Productions Ltd | Arts & recreation | 2025 |
| HD Shine Ltd | Construction | 2021 |
| Hd-Hv Limited | Construction | 2026 |
| Hdrm Limited | Information & communication | 2011 |
| Headway Darlington & District | Health & social care | 2015 |
| Healthwatch Darlington Limited | Health & social care | 2013 |
| Heart Hairdressing Limited | Other services | 2016 |
| Hedera Consulting Limited | Other services | 2003 |
| Hedgeside Farm Produce Limited | Agriculture & fishing | 2013 |
| Hedley & Hedley Ltd | Real estate | 2025 |
| Hedleys of Darlington Ltd | Manufacturing | 2022 |
| Heffs Ltd | Construction | 2024 |
| Heighington PUB Company Ltd | Hospitality | 2024 |
| Hejab Tawfiq Exporting Ltd | Wholesale & retail | 2025 |
| Helios People Development Limited | Professional & scientific | 2003 |
| Help File IT Ltd | Professional & scientific | 2025 |
| Helphire EBT Trustee Limited | Other services | 1999 |
| Hemmings Plumbing & Heating Ltd | Construction | 2025 |
| Henley Home Interiors Limited | Other services | 2022 |
| Henry James Building (North East) Ltd | Construction | 2022 |
| Henshaw Aviation Limited | Administrative & support | 2021 |
| Henson Investments Ltd | Real estate | 2013 |
| Hepy Ltd | Wholesale & retail | 2025 |
| Hering Developments Ltd | Extraterritorial | 2017 |
| Heritage Court (Darlington) RTM Company Limited | Households | 2009 |
| Heritage Court Management Company (Darlington) Limited | Households | 2005 |
| Heritage Healthcare Franchising Limited | Administrative & support | 2012 |
| Heritage Healthcare International Franchising Limited | Administrative & support | 2017 |
| Heritage Healthcare Limited | Financial services | 2007 |
| Heritage House Ripon Limited | Professional & scientific | 2018 |
| Heritage House Surveys LLP | | 2020 |
| Heronpeak Developments Limited | Real estate | 1984 |
| Herring-Sykes Limited | Wholesale & retail | 2017 |
| Heseltine Limited | Wholesale & retail | 2025 |
| Hewitson Property Services Ltd | Construction | 2023 |
| Hewitt Chadwick Partnership Limited | Real estate | 2020 |
| Hewitt Property Ltd | Real estate | 2020 |
| HEX Holdings Limited | Financial services | 2025 |
| Hexxon UK Ltd | Professional & scientific | 2017 |
| HG Gate House Limited | Professional & scientific | 2010 |
| HGC Services Limited | Administrative & support | 2023 |
| HGS Trading Ltd | Wholesale & retail | 2019 |
| HGT Building & Refurbishment Ltd | Construction | 2024 |
| HGT Construction Services Limited | Construction | 2020 |
| Hgwind Ltd | Manufacturing | 2026 |
| HH & S Enterprises Ltd | Wholesale & retail | 2017 |
| HH FOX Ltd | Hospitality | 2025 |
| HHH Property Management Limited | Real estate | 2021 |
| HHL Knight Ltd | Information & communication | 2023 |
| HHW International Holdings Limited | Wholesale & retail | 2020 |
| HI 5 Standard Ltd | Wholesale & retail | 2021 |
| HI OM Subco Limited | Health & social care | 2026 |
| Hials Ltd | Financial services | 2016 |
| Higginsy Limited | Wholesale & retail | 2025 |
| High ASH Drive Flat Management Company Limited | Households | 2000 |
| High END Close Management Limited | Households | 2025 |
| High Grade Hydroponics Ltd | Wholesale & retail | 2018 |