| A & M Carling Properties Limited | Real estate | 2025 |
| A Layfield Farms Ltd | Agriculture & fishing | 2022 |
| A P Company Recovery Ltd | Wholesale & retail | 2022 |
| A Training Safety Advice Service Limited | Other services | 2017 |
| A1 Cosmetic Car Care Limited | Wholesale & retail | 2002 |
| AAA LAB Ltd | Professional & scientific | 2024 |
| Abbeywood Property Investments Limited | Real estate | 2019 |
| Abbeywood Property Management Ltd | Real estate | 2025 |
| Access for Business (North East) Limited | Professional & scientific | 1999 |
| Access for Business Limited | Professional & scientific | 2001 |
| Adam's Pizzeria Willington Ltd | Hospitality | 2019 |
| Adamson Consulting Limited | Professional & scientific | 2024 |
| Aedro Limited | Information & communication | 2018 |
| Aedro Solutions Limited | Professional & scientific | 2023 |
| Aghoco 1085 Limited | Professional & scientific | 2012 |
| AIM Straight Alignments Ltd | Wholesale & retail | 2023 |
| AJ Pizza Restaurant Limited | Hospitality | 2025 |
| Alchimia Ltd | Professional & scientific | 2018 |
| Aldworth North Properties Limited | Real estate | 2020 |
| Alpha Rail Engineering Limited | Professional & scientific | 2004 |
| AML Performance Cars Ltd | Wholesale & retail | 2023 |
| Amsap Security Limited | Information & communication | 2009 |
| Andrew Carling Electrics Ltd | Construction | 2024 |
| Applebycatering Ltd | Hospitality | 2025 |
| Arch Transport Services Ltd | Transport & logistics | 2025 |
| Archangel SP Ltd | Wholesale & retail | 2015 |
| ARH Developments Limited | Professional & scientific | 2015 |
| Arktree Ltd | Wholesale & retail | 2023 |
| Arnies Plumbing Services Ltd | Construction | 2024 |
| Arya Global Associates Limited | Real estate | 2020 |
| Ashsouth Limited | | 1984 |
| ASK Estates Group Ltd | Real estate | 2024 |
| Assent Accountants Limited | Professional & scientific | 2018 |
| Auction North Limited | Real estate | 2017 |
| AVA Restaurant Ltd | Hospitality | 2025 |
| Avena Healthcare Services Ltd | Professional & scientific | 2023 |
| AVI Restaurant Ltd | Hospitality | 2025 |
| Avmm Inspection Limited | Manufacturing | 2024 |
| AWC Construction Ltd | Construction | 2023 |
| B B P (Durham) Limited | Professional & scientific | 2018 |
| B7 Developments Limited | Real estate | 2026 |
| Balanced Support Reins Ltd | Manufacturing | 2019 |
| Beacon Translations Limited | Professional & scientific | 1992 |
| Beechburn Home Improvements Ltd | Construction | 2016 |
| Bend Over Backwards Yoga Ltd | Other services | 2022 |
| BF Lettings Ltd | Real estate | 2021 |
| BHR Brickwork Ltd | Construction | 2019 |
| Bishop Auckland and District Angling Club | Agriculture & fishing | 1996 |
| Bishopsgarth Interim Ltd | Professional & scientific | 2009 |
| BIT Studios Ltd | Information & communication | 2020 |
| Blaze Plumbing & Heating Limited | Construction | 2026 |
| Blind Life in Durham | Other services | 2008 |
| Blue Ferret Limited | Agriculture & fishing | 2021 |
| Bodywork Direct Limited | Wholesale & retail | 2006 |
| Boze Games Limited | Information & communication | 2014 |
| Brighton Rock Productions Limited | Arts & recreation | 2016 |
| Broomy Developments Ltd | Construction | 2025 |
| BSJ Innovate Ltd | Professional & scientific | 2018 |
| Built by Mays Ltd | Information & communication | 2023 |
| Buston & Maughan Limited | Construction | 2005 |
| Bybwoods Ltd | Wholesale & retail | 2025 |
| C N K Civils Ltd | Construction | 2008 |
| C&A Construction & Maintenance Limited | Construction | 2016 |
| C-Cubed Logistics Limited | Transport & logistics | 2020 |
| Cactus Corporation Limited | Hospitality | 2021 |
| Cailes Builders Ltd | Construction | 2021 |
| Cailes Homes Ltd | Real estate | 2023 |
| Caniko Ltd | Hospitality | 2026 |
| Canny Digital Ltd | Information & communication | 2023 |
| Caspian Renovations Ltd | Construction | 2026 |
| Cathedral Lock and Safe Services Limited | Construction | 2004 |
| Cathedral Wholesale and Events Limited | Wholesale & retail | 2018 |
| Cavaze Property Improvements Ltd | Construction | 2019 |
| CCL (Events) Ltd | Education | 2017 |
| Cedar Casetta Ltd | Hospitality | 2020 |
| Chalkies Sports Bar Ltd | Hospitality | 2025 |
| Changing Step (North East) C.I.C. | Health & social care | 2015 |
| Charlotte Leigh Ltd | Real estate | 2025 |
| Cheema Fish Grill Ltd | Hospitality | 2025 |
| Cherry Tree Lettings Ltd | Real estate | 2018 |
| CJW Site Solutions Limited | Construction | 2018 |
| CL Engineering Services (Uk-Ne) Ltd | Professional & scientific | 2025 |
| Clark Recruitment Group Ltd | Administrative & support | 2020 |
| Clement Haulage Limited | Transport & logistics | 2005 |
| Clemitsons Limited | Wholesale & retail | 1998 |
| Cliff & Gristwood Ltd | Transport & logistics | 2002 |
| Clover Transport Ltd | Transport & logistics | 2022 |
| Cmca Integrated Systems Limited | Manufacturing | 2014 |
| CML Property Solutions Limited | Real estate | 2013 |
| COD FRY 07 Ltd | Hospitality | 2024 |
| Coffea Espression Ltd | Manufacturing | 2023 |
| Compex Hazardous Inspection Ltd | Energy | 2014 |
| Cornerstone Supported Housing & Counselling Ltd | Health & social care | 2010 |
| Correct Resources Ltd | Real estate | 2025 |
| Cowley Asset Finance Limited | Financial services | 2019 |
| Coxon Business Partners Ltd | Professional & scientific | 2025 |
| Craidle Intelligence Group Ltd | Information & communication | 2025 |
| Craig W Assessment Ltd | Professional & scientific | 2023 |
| Crook Barber Ltd | Other services | 2025 |
| Crook Community Leisure Limited | Health & social care | 2013 |