| Adverse Money Limited | Financial services | 2019 |
| Advimate Ltd | Information & communication | 2016 |
| Adwani Motors Limited | Water & waste | 2022 |
| Aendil Ltd | Health & social care | 2026 |
| AES Darlington Limited | Other services | 2024 |
| AES Property Ltd | Real estate | 2019 |
| AFB Trading Limited | Wholesale & retail | 2012 |
| AFFILI8 Marketing Limited | Information & communication | 2020 |
| Affordable Homes Group Limited | Construction | 2015 |
| AFR Cleveland Ltd | Real estate | 2014 |
| Afri Aroma Ltd | Manufacturing | 2025 |
| Afroc Deli Limited | Hospitality | 2020 |
| AG Darlington Limited | Other services | 2024 |
| AG Logistics and Services Ltd | Transport & logistics | 2026 |
| AG Lucia Ltd. | Professional & scientific | 2018 |
| Agastya Foods Limited | Hospitality | 2025 |
| AGE UK North Yorkshire & Darlington | Health & social care | 2009 |
| Agency Systems Limited | Real estate | 2003 |
| Aghoco 1136 Limited | Wholesale & retail | 2012 |
| Aglow Heating Ltd | Construction | 2023 |
| AGO Asset Management Limited | Households | 2023 |
| AGR Transport Limited | Transport & logistics | 2016 |
| Agri Services North East Limited | Administrative & support | 2022 |
| Agri-Fiber Board (Holdings) Ltd | Manufacturing | 2020 |
| Agri-Fiber Board Ltd | Manufacturing | 2020 |
| AGRICORE2 Ltd | Water & waste | 2021 |
| Agriflow Land and Water Ltd | Administrative & support | 2025 |
| Agristall Limited | Professional & scientific | 2024 |
| AH Commercial Consultancy Ltd | Information & communication | 2012 |
| AH Property Improvements Ltd | Construction | 2022 |
| AH Windtech Ltd | Construction | 2026 |
| Ahcr Properties Ltd | Real estate | 2019 |
| AHH Holdings Ltd | Construction | 2023 |
| Ahlouise Ltd | Wholesale & retail | 2024 |
| Aiaron Limited | Wholesale & retail | 2025 |
| Aiden Sea Products Limited | Wholesale & retail | 2005 |
| AIE Assets Limited | Financial services | 2025 |
| AIM Design Ltd | Professional & scientific | 2018 |
| Aimee Briggs Ltd | Health & social care | 2023 |
| Aimee Brown Hairdressing Ltd | Other services | 2019 |
| Ainsliem Ltd | Wholesale & retail | 2024 |
| Air Charter Executive Ltd | Transport & logistics | 2014 |
| Air Dispatch Solutions Ltd | Transport & logistics | 2023 |
| Aircraft Hire Limited | Administrative & support | 2024 |
| Airey Project Services Limited | Information & communication | 2022 |
| Airport Hills Ltd | Other services | 2011 |
| Airport Safeguarding Limited | Professional & scientific | 2020 |
| AIS Surveyors Ltd | Professional & scientific | 1997 |
| AJ Highway Consultancy Ltd | Professional & scientific | 2017 |
| AJ Luxury Travel Ltd | Administrative & support | 2025 |
| AJ Plates Ltd | Manufacturing | 2024 |
| AJ Property Development and Rentals Limited | Real estate | 2025 |
| AJB Signalling Limited | Construction | 2019 |
| Ajes Property Solutions Limited | Other services | 2019 |
| AJH Hygiene & Therapy Ltd | Health & social care | 2019 |
| AJK Rail Limited | Manufacturing | 2024 |
| AJS & Daughter Limited | Manufacturing | 2014 |
| AJS Business Services (NE) Ltd | Administrative & support | 2025 |
| AJS Law LLP | | 2023 |
| AJS Projects at Your Service Limited | Construction | 2024 |
| AJW Grounds Maintenance Ltd | Other services | 2023 |
| AK Moves Limited | Transport & logistics | 2024 |
| AKA Hill Ltd | Financial services | 2024 |
| AKA Installations Limited | Construction | 2012 |
| Akrigg Holdings Limited | Real estate | 2023 |
| Akshar (N.E.) Ltd | Wholesale & retail | 2013 |
| Aksimi Trading Ltd | Wholesale & retail | 2025 |
| AL Anwar KMH Ltd | Wholesale & retail | 2025 |
| AL Comms Ltd | Information & communication | 2026 |
| AL Rasheed Supermarket Limited | Wholesale & retail | 2016 |
| Alan Wadkins Limited | Wholesale & retail | 1966 |
| Albert Hill Commercials Limited | Wholesale & retail | 2000 |
| Albertgate Management Company Limited | Households | 2006 |
| Aldaja Payment Solutions Ltd | Administrative & support | 2018 |
| Aldbrough Hall Properties | | 1998 |
| Alex Aqua JET Wash Limited | Administrative & support | 2025 |
| Alex Austin Flooring Ltd | Construction | 2023 |
| Alex Nitu Ltd | Transport & logistics | 2019 |
| Alex Rome Limited | Information & communication | 2015 |
| Alex Thomas Property Services Ltd | Real estate | 2020 |
| Alexander IT Ltd | Information & communication | 2016 |
| Alexander Macmurray Catering Ltd | Hospitality | 2010 |
| Alfass Ltd | Transport & logistics | 2017 |
| Alfidore Ltd | Real estate | 2025 |
| Alfresco Leisure Direct Ltd | Wholesale & retail | 2023 |
| Alibail Ltd | Financial services | 2024 |
| Alice & Astrid Limited | Manufacturing | 1998 |
| Alinefituk Ltd | Wholesale & retail | 2025 |
| Alishan (Wisbech) Ltd | Hospitality | 2006 |
| Alisher Electricians Limited | Manufacturing | 2024 |
| ALJ Property Investment Ltd | Real estate | 2021 |
| Alkea Consultants Ltd | Extraterritorial | 2024 |
| ALL Access Inspections Ltd | Manufacturing | 2018 |
| ALL Aspect Safety Ltd | Construction | 2025 |
| ALL in the Deets Limited | Construction | 2025 |
| ALL Saints Mews Management Company Limited | Real estate | 2004 |
| ALL Saints Millennium Trust (Darlington) Limited | Arts & recreation | 1997 |
| ALL Sign Solutions Limited | Manufacturing | 2003 |
| ALL Signs Direct Ltd | Manufacturing | 2020 |
| All-Purpose Academy Ltd | Wholesale & retail | 2026 |