| ALL Mine Investments Limited | Financial services | 2026 |
| Ashfield Interiors (Durham) Limited | Construction | 2013 |
| B. & R. Glazing Company Limited | Construction | 1965 |
| Brennan & Coates (Haulage) Limited | Transport & logistics | 1983 |
| Calendar Properties Limited | Professional & scientific | 2011 |
| Calendar Windows Limited | Other services | 1990 |
| Develop Durham Ltd | Real estate | 2025 |
| Durham Air Conditioning Ltd. | Construction | 1999 |
| Esprit HAB Limited | Other services | 2015 |
| Groundshire North East Limited | Administrative & support | 2020 |
| GWS Holdings Limited | Financial services | 2016 |
| Humphreys Wealth Management Limited | Financial services | 2026 |
| Kensington Gardens Ltd | Construction | 2017 |
| Langley Moor Car Valeting Centre Ltd | Wholesale & retail | 2018 |
| Littleburn Property Company Limited | Professional & scientific | 2005 |
| LLD (1) Ltd | Real estate | 2023 |
| Melanie Matthews Ltd | Professional & scientific | 2026 |
| Military Incorporated Ltd | Wholesale & retail | 2025 |
| NK Aesthetics Ltd | Other services | 2022 |
| Oasis Hospitality Training CIC | Health & social care | 2026 |
| Pennington Funeral Services Limited | Other services | 1946 |
| Premiership Clubs Limited | Hospitality | 2017 |
| Regent Decorators Holdings Limited | Professional & scientific | 2016 |
| Safe & Sure Fire Protection Limited | Manufacturing | 1994 |
| Scott Racing Limited | Professional & scientific | 2001 |
| Sirius Civil Engineering Limited | Construction | 2004 |
| Sirius Environmental Ltd | Water & waste | 2009 |
| Siriusecodev (Minety) Ltd | Energy | 2022 |
| SQM Solutions Limited | Professional & scientific | 2002 |