| Concept Aesthetics Limited | Health & social care | 2006 |
| Consolidated Mortgages Ltd | Financial services | 1997 |
| Contractgain Limited | Wholesale & retail | 2004 |
| Covenant Publishing Company Limited | Information & communication | 1987 |
| Cutting Loose Ltd | Other services | 2003 |
| D & L Cummings Limited | Financial services | 2022 |
| D P Cyclone Sales Limited | Professional & scientific | 1976 |
| D.W.S. Property Developments Limited | Construction | 2004 |
| Daleview Holiday Park Limited | Hospitality | 2020 |
| Danap Properties Limited | Real estate | 2021 |
| Danebank Limited | Real estate | 2004 |
| Danssam Limited | Other services | 2001 |
| Darlington & Simpson Rolling Mills Social Club Ltd | Hospitality | 1999 |
| Darlington Door Services Limited | Construction | 1999 |
| Darlington Rugby Football Club Limited | Arts & recreation | 1996 |
| Darlington Supported Housing Limited | Health & social care | 1999 |
| Dasyl Enterprises Limited | Professional & scientific | 1982 |
| David Ludlow Limited | Wholesale & retail | 2001 |
| Deansgate Properties Limited | Construction | 1993 |
| Deerness Kennels Limited | Agriculture & fishing | 2006 |
| Delta - North Consett Limited | Education | 1998 |
| Denton Hall Racing Limited | Arts & recreation | 2002 |
| Derwent Garden Management Company Limited | Households | 2004 |
| Derwent Reservoir Sailing Club Limited | Arts & recreation | 1967 |
| Devon Conversions Limited | Manufacturing | 1990 |
| Discovery PPC Limited | Information & communication | 2020 |
| Diversitech Group Limited | Administrative & support | 2003 |
| DJ Camp Ltd | Manufacturing | 2005 |
| DLI Group Ltd | Administrative & support | 2017 |
| Doby Verrolec Limited | Professional & scientific | 1998 |
| Dolmanbury Limited | Wholesale & retail | 1982 |
| Dovecron Limited | Wholesale & retail | 1999 |
| Dufell Scaffolding Company Limited | Construction | 2020 |
| DUO for MEN Limited | Administrative & support | 1997 |
| Durham Decorators (North East) Limited | Construction | 1999 |
| Durham Interiors (Auckland) Limited | Manufacturing | 2006 |
| Durham Soap Company Ltd | Other services | 2017 |
| Durham Specsavers Limited | Wholesale & retail | 1996 |
| Durham Vineyard | Other services | 2006 |
| E.B. & C.A. Welsh Limited | Hospitality | 2006 |
| East Durham Estates Limited | Real estate | 2018 |
| Ebac Appliances Ltd | Professional & scientific | 1987 |
| Ebac Group Limited | Administrative & support | 1997 |
| Ebac Limited | Manufacturing | 1973 |
| Ediscum Properties Limited | Real estate | 1960 |
| Educational Publishing Services Limited | Professional & scientific | 2005 |
| Eggleston Hall Gardens | | 2001 |
| Electrix International Limited | Manufacturing | 1981 |
| Emerald Management Consultants Limited | Real estate | 1997 |
| Endeavour 149 Limited | Construction | 2017 |
| Enhance DRY Cleaning Limited | Other services | 2002 |
| Enzo Ltd | Other services | 2003 |
| Eppleton Quarry Products (Scunthorpe) Limited | Mining & quarrying | 2002 |
| ESH Winning Football Club Limited | Arts & recreation | 2017 |
| ETB (North East) Limited | Financial services | 2026 |
| Evokation Limited | Manufacturing | 2003 |
| Ezimix Limited | Manufacturing | 2001 |
| Fabweld Structures (NE) Ltd | Manufacturing | 2026 |
| Fast-Fit Express Limited | Wholesale & retail | 1998 |
| Filemark Limited | Administrative & support | 2002 |
| Finishing Touch Clinic Limited | Other services | 2003 |
| Firthmoor Fisheries Limited | Hospitality | 2002 |
| Forge Technology Limited | Construction | 1994 |
| Foster Cares Ltd | Health & social care | 2004 |
| Fourward Developments (UK) Limited | Professional & scientific | 1993 |
| FPC (Darlington) Owners Limited | Real estate | 1997 |
| Fred Foster Transport Limited | Transport & logistics | 2000 |
| Fuel Mistake Ltd | Wholesale & retail | 2020 |
| G W Leader Property Limited | Real estate | 2003 |
| G. B. U Limited | Extraterritorial | 2005 |
| G.B.P. (North East) Limited | Construction | 1999 |
| G.R. & D. Herbert Limited | Agriculture & fishing | 1978 |
| Games Galaxy Retail Ltd | Administrative & support | 2016 |
| Gary Chambers Ltd | Other services | 2002 |
| Gateopen Limited | Wholesale & retail | 2004 |
| GDM Food and Wine Ltd | Wholesale & retail | 2021 |
| GEB Enterprises Ltd | Other services | 2022 |
| George Kerr Trading Ltd | Wholesale & retail | 2017 |
| Gilligan Fabrications Limited | Manufacturing | 1986 |
| Glenn Muller Plumbing & GAS Services Limited | Construction | 2004 |
| Grafts and Wycliffe Ltd | Real estate | 2024 |
| Grava Core Ltd | Construction | 2025 |
| Green Lane Nursery and Child Care Centre | Education | 2001 |
| Growth Capital Ventures Nominees (AB) Limited | Financial services | 2017 |
| Growth Capital Ventures Nominees Limited | Financial services | 2013 |
| GTJ Services Ltd | Real estate | 2005 |
| Hackett & Baines Limited | Wholesale & retail | 2003 |
| Hall Farm Foods Limited | Wholesale & retail | 2006 |
| HAR Transport Limited | Transport & logistics | 1994 |
| Hardman Ross Limited | Professional & scientific | 2001 |
| Haswell Moor Developments Ltd | Construction | 2007 |
| Hathaway Roofing Limited | Construction | 1997 |
| Hayley Louise Limited | Wholesale & retail | 2025 |
| Hblt Limited | Transport & logistics | 2003 |
| Hc-One Management Limited | Professional & scientific | 2021 |
| HE Oban Limited | Hospitality | 2024 |
| Hedley Davis Property & Development Company Limited | Real estate | 1999 |
| Heritage East Limited | Extraterritorial | 2003 |
| Heritage North Limited | Professional & scientific | 2001 |
| Heritage South Limited | Construction | 2003 |