| Autofix Pro Ltd | Wholesale & retail | 2025 |
| Autoglaze Darlington Limited | Wholesale & retail | 2008 |
| Autohub Central Ltd | Wholesale & retail | 2025 |
| Automating the 'Automation' Limited | Administrative & support | 2014 |
| Auton House Vehicles Limited | Wholesale & retail | 2015 |
| Auxillis Limited | Financial services | 1994 |
| AV Joinery Services Limited | Construction | 2008 |
| AVA Beauty & Aesthetics Ltd | Other services | 2025 |
| AVA Invest (North East) Ltd | Construction | 2022 |
| Avant Developments NE Ltd | Construction | 2024 |
| Avanti Motors Ltd | Wholesale & retail | 2022 |
| Avatar Machinery Ltd | Wholesale & retail | 2022 |
| Avatar Partnership LLP | | 2023 |
| AVD Financial Services Ltd | Financial services | 2026 |
| AVD Holding Group Ltd | Financial services | 2025 |
| Aventus Property Management Ltd | Households | 2025 |
| Averiqlof Ltd | Information & communication | 2026 |
| AW Building Projects North East Ltd | Administrative & support | 2023 |
| AW Fabrication Limited | Manufacturing | 1992 |
| AW Tiling Limited | Construction | 2019 |
| Awaken Consulting & Training Services Limited | Education | 2004 |
| Awaken School of Outcome Oriented Psychotherapies Limited | Education | 2006 |
| AWG Motors Ltd | Wholesale & retail | 2019 |
| Awis Trans Ltd | Transport & logistics | 2021 |
| AWR Darlington Ltd | Wholesale & retail | 2024 |
| AX Store Limited | Wholesale & retail | 2024 |
| AXE Holdings Ltd | Information & communication | 2016 |
| Axeltucker Ltd | Other services | 2025 |
| Axion Energy Solutions Ltd | Professional & scientific | 2011 |
| Axis Psychology Limited | Health & social care | 2025 |
| Ayala Enterprise Ltd | Real estate | 2017 |
| Aycliffe Business Park Community Limited | Other services | 2016 |
| Aycliffe Filtration Limited | Manufacturing | 2009 |
| Ayla Coffee House Ltd | Hospitality | 2023 |
| Ayton Logistics Ltd | Transport & logistics | 2025 |
| Ayton Property Limited | Hospitality | 2007 |
| Azzurro 58 Ltd | Extraterritorial | 2012 |
| B & C Building Contractors Ltd | Construction | 2012 |
| B & C Property (North East) Ltd | Real estate | 2020 |
| B & M Roofing & Sons Limited | Construction | 2023 |
| B & S Market N Ltd | Wholesale & retail | 2024 |
| B a Property and Investments Limited | Real estate | 2025 |
| B B F S Blaydon Biomass Fuel Supplies Ltd | Manufacturing | 2024 |
| B L Logistics Limited | Construction | 2019 |
| B L Training (Holdings) Limited | Professional & scientific | 2008 |
| B L Training Limited | Education | 1998 |
| B Mansley Productions Ltd | Information & communication | 2024 |
| B Marshall Holdings Ltd | Financial services | 2021 |
| B&M Leadworks Ltd | Construction | 2026 |
| B&T Cladding Limited | Construction | 2024 |
| B&T Humble Abode Limited | Real estate | 2025 |
| B.A Sports Bar Ltd | Hospitality | 2024 |
| B.B Enterprising Ltd | Administrative & support | 2018 |
| B.I. Cross Solutions Ltd. | Information & communication | 2012 |
| B.M.A. Properties Limited | Hospitality | 2007 |
| B2B Identity Ltd | Professional & scientific | 2026 |
| BA Engineer Ltd | Construction | 2016 |
| Baba Parcel Express Ltd | Transport & logistics | 2026 |
| Babat Properties Ltd | Financial services | 2021 |
| Babul's (Darlington) Ltd | Hospitality | 2021 |
| Babul's (Durham) Limited | Hospitality | 2025 |
| Babul’S (Teesdale) Limited | Hospitality | 2022 |
| BAC Office Equipment Limited | Wholesale & retail | 1995 |
| BACK2BALANCE (NE) Limited | Health & social care | 2017 |
| BAD Planet Limited | Information & communication | 2021 |
| Badger Heating & Plumbing Services Limited | Construction | 2019 |
| BAG Honey Productions Ltd | Information & communication | 2023 |
| Bailey's of Witham Limited | Financial services | 2024 |
| Bainbridge Land & Letting Ltd | Real estate | 2025 |
| Bainbridge Marketing Ltd | Information & communication | 2015 |
| Baked Steel Limited | Manufacturing | 2022 |
| Baker People CIC | Manufacturing | 2019 |
| Bakerk Limited | Wholesale & retail | 2025 |
| Bales Buddies Therapy Dogs Ltd | Other services | 2019 |
| Baltic Training Services Limited | Education | 2006 |
| Baltik Service Limited | Transport & logistics | 2025 |
| Bamboozles Adventure World Limited | Arts & recreation | 2009 |
| Bambridge Heating Ltd | Construction | 2023 |
| Bambudda Ltd | Hospitality | 2017 |
| Bancroft Maritime Security Solutions Limited | Administrative & support | 2009 |
| Banklands Court Residents Association Limited | Hospitality | 1994 |
| Bankside Court Management Company (Darlington) Limited | Households | 2007 |
| Bannatyne Brand Management (Holdings) Limited | Professional & scientific | 2023 |
| Bannatyne Finance Limited | Financial services | 2019 |
| Bannatyne Fitness (2) Limited | Arts & recreation | 2011 |
| Bannatyne Fitness (6) Limited | Extraterritorial | 1995 |
| Bannatyne Fitness (7) Limited | Extraterritorial | 1990 |
| Bannatyne Fitness (8) Limited | Extraterritorial | 1993 |
| Bannatyne Fitness Limited | Arts & recreation | 1996 |
| Bannatyne Hotels Limited | Hospitality | 1996 |
| Bannatyne Media Limited | Information & communication | 2005 |
| Bannatyne Properties Limited | Real estate | 2011 |
| Bannatyne's Health Club (Blackpool) Ltd | Extraterritorial | 2000 |
| Bannatyne's Health Club (Falkirk) Limited | Extraterritorial | 1998 |
| Bannatyne's Health Club (Fife) Limited | Extraterritorial | 1998 |
| Bannatyne's Health Club (Norwich West) Limited | Arts & recreation | 2016 |
| Bannatyne's Health Club (Tower 42) Ltd | Extraterritorial | 2003 |
| Bannatyne's Health Club Limited | Extraterritorial | 1998 |
| Banner Contracts (Halnaby) Limited | Mining & quarrying | 1993 |
| Banner Holdings (Halnaby) Limited | Financial services | 2018 |