| Darkwell Limited | Construction | 1983 |
| Darren O'Beirne Ltd | Professional & scientific | 2018 |
| Dartmouth Brands Ltd | Wholesale & retail | 2013 |
| Datamono Ltd | Information & communication | 2021 |
| Datum Contracts International Limited | Manufacturing | 1967 |
| Datum Point Electrical Ltd | Construction | 2020 |
| Davenport Place RTM Company Limited | Households | 2011 |
| David Brown Waste Management Ltd | Administrative & support | 2026 |
| David Fleetwood Ltd | Professional & scientific | 2017 |
| David James Holdings Limited | Arts & recreation | 2021 |
| David P Elder Consultancy Limited | Other services | 2022 |
| Davies & Green Ltd | Construction | 2013 |
| DAX Pharma Limited | Professional & scientific | 2020 |
| Daybat Limited | Information & communication | 2015 |
| DBT Consulting Limited | Information & communication | 2010 |
| DCL Consulting and Investments Limited | Households | 2016 |
| Ddgh Equities LLP | | 2016 |
| Dead MAN Walking Limited | Construction | 2020 |
| Debut Academy Hertford Limited | Education | 2024 |
| Debut Hertford Salon LLP | | 2025 |
| Deck Converters Limited | Wholesale & retail | 2017 |
| Declan Accardi Volt Ltd | Wholesale & retail | 2026 |
| DECOR8 Paint Effects Limited | Construction | 2010 |
| DEE Maak Ltd | Hospitality | 2024 |
| Deejay Taxis Limited | Transport & logistics | 2019 |
| Define Digital Ltd | Information & communication | 2017 |
| Degraf Digital Solutions Ltd | Manufacturing | 2015 |
| Delaney Hospitality Limited | Health & social care | 2026 |
| Delgado Capital Limited | Administrative & support | 2015 |
| Delgado Holdings Limited | Professional & scientific | 2017 |
| DEM Trading Limited | Other services | 2024 |
| Demeter Earth Limited | Professional & scientific | 2022 |
| Denimoz Ltd | Wholesale & retail | 2024 |
| Derby Manor Leisure Ltd | Hospitality | 2024 |
| Derby Manor Properties Ltd | Real estate | 2018 |
| Dermatech (UK) Limited | Other services | 2008 |
| Destination Study UK Ltd | Education | 2025 |
| Detort Limited | Health & social care | 2012 |
| Deuk Solutions Limited | Wholesale & retail | 2019 |
| Devils Edge Shirt Company Limited | Administrative & support | 2014 |
| Devstefops Ltd | Information & communication | 2022 |
| Devvine Studios Ltd. | Information & communication | 2022 |
| Dewar & Wilson Ltd | Professional & scientific | 2025 |
| DG Transport Limited | Transport & logistics | 2025 |
| DG Wright Properties Ltd | Real estate | 2016 |
| DGL Workshop Supplies Ltd | Wholesale & retail | 2012 |
| DHC D3NTAL Ltd | Health & social care | 2013 |
| Dicker Mill Investments Limited | Real estate | 1964 |
| Dicker Mill Management Company Limited | Real estate | 1986 |
| Diddlydory Ltd | Administrative & support | 2015 |
| Differential Audio Limited | Information & communication | 2008 |
| Differential Properties Ltd | Real estate | 2025 |
| DIG My BED Limited | Manufacturing | 2016 |
| Digiconex Limited | Wholesale & retail | 2013 |
| Digital Infinity Limited | Information & communication | 2014 |
| Digital Laundry Solutions Ltd | Manufacturing | 2022 |
| Digital Media Studio Limited | Information & communication | 2015 |
| Digital Media Technologies Ltd | Information & communication | 2011 |
| Digital Media Technology Group Limited | Professional & scientific | 2021 |
| Digression Limited | Professional & scientific | 2007 |
| Dimka Limited | Manufacturing | 2020 |
| Dinos Properties Ltd | Real estate | 2026 |
| Diosynvax Ltd. | Health & social care | 2017 |
| Direct Carpets Limited | Wholesale & retail | 2012 |
| Direct Laundry Rentals Limited | Administrative & support | 1996 |
| Direct Luxury Car Hire Ltd | Administrative & support | 2020 |
| Direct Mobility (UK) Limited | Professional & scientific | 1999 |
| Direct Mobility Hire Ltd | Professional & scientific | 2006 |
| Direct Mobility Solutions Limited | Other services | 2004 |
| Direct Mortgage Solutions Limited | Financial services | 2022 |
| Direct Scaffolding Contractors Limited | Construction | 2006 |
| Direct Tiles (Nazeing) Limited | Wholesale & retail | 2023 |
| Disco Ltd | Information & communication | 2025 |
| Discountstoragesolutions Ltd | Wholesale & retail | 2022 |
| Displaybase Limited | Information & communication | 2002 |
| Dispute Vitae Limited | Professional & scientific | 2016 |
| Distinction Flooring Ltd | Construction | 2019 |
| Divide Events Ltd | Arts & recreation | 2024 |
| DJS Education Services Ltd | Administrative & support | 2022 |
| DK Thermal Limited | Extraterritorial | 1999 |
| DKC Haulage Limited | Transport & logistics | 2015 |
| DKK Consulting Ltd | Professional & scientific | 2026 |
| DL Graphics Creative Limited | Manufacturing | 2014 |
| DLH Projects Limited | Construction | 2015 |
| DLM Composites & GRP Ltd | Manufacturing | 2018 |
| DM Builders & Contractors Ltd | Construction | 2013 |
| DM Mechanical Ltd | Wholesale & retail | 2012 |
| DMG Design Services Ltd | Construction | 2024 |
| Dmsldn Ltd | Construction | 2003 |
| DNA Herts Property Management Limited | Real estate | 2021 |
| Dna-Play Limited | Manufacturing | 2010 |
| DO Some Digital Limited | Professional & scientific | 2022 |
| DOE Official Ltd | Wholesale & retail | 2022 |
| Doggy Stylers Ltd | Other services | 2025 |
| Doherty Ltd | Other services | 2024 |
| DOI Group Limited | Construction | 1997 |
| DOI Holdings Limited | Financial services | 2018 |
| DOI Properties Limited | Financial services | 2018 |
| DOI Property Holdings Limited | Real estate | 2017 |
| Dolphin Court Management Company (Hertford) Limited | Households | 2008 |