| 12 Marine Parade Folkestone Management Company Limited | Households | 2014 |
| 1901 Catering Ltd | Hospitality | 2022 |
| 1968 Limited | Information & communication | 2010 |
| 1NE Properties Ltd | Real estate | 2023 |
| 23 MR Limited | Administrative & support | 2022 |
| 2S-COTTAGES Ltd | Hospitality | 2022 |
| 3 C Excavation Limited | Construction | 2022 |
| 3 C Services Group Limited | Financial services | 2025 |
| 3 C Services Limited | Construction | 2017 |
| 360 Air Maps Ltd | Professional & scientific | 2020 |
| 3D Rhino Ltd | Manufacturing | 2024 |
| 4S Event Solutions Ltd | Wholesale & retail | 2025 |
| 50 Bridge Street Morpeth Limited | Hospitality | 2025 |
| 55 Degree Developments Ltd | Construction | 2025 |
| 55 Degrees Contracting Limited | Information & communication | 2025 |
| 6 Needham Road Limited | Professional & scientific | 2004 |
| 6-S Performance Ltd | Arts & recreation | 2018 |
| 60 Smarter Ltd | Other services | 2017 |
| 6TIMES9 Ltd | Administrative & support | 2019 |
| 70 West Street Old Market Management Company Limited | Households | 1989 |
| 7T8 Ltd | Real estate | 2018 |
| @Wann Touring Ltd | Arts & recreation | 2020 |
| A & B Taxi Services Limited | Transport & logistics | 2003 |
| A & E Ambulance Sales Limited | Wholesale & retail | 2024 |
| A & K Financial Management Limited | Financial services | 2017 |
| A & K Productions Ltd | Arts & recreation | 2026 |
| A Full House Ltd | Construction | 2021 |
| A H Scaffolding Services Limited | Construction | 2015 |
| A K M Highway Services Limited | Other services | 2014 |
| A Liberty Life Ltd | Professional & scientific | 2006 |
| A Plus Efficiency Ltd | Construction | 2016 |
| A Shafiq Limited | Health & social care | 2018 |
| A Special-Something Limited | Wholesale & retail | 2025 |
| A T Robson Limited | Agriculture & fishing | 2023 |
| A&E Tyre, Exhaust & Service Centre Limited | Wholesale & retail | 2013 |
| A&S Properties N.E Limited | Real estate | 2024 |
| A. Benson Properties Limited | Construction | 2007 |
| A. G. Waugh and Sons Limited | Agriculture & fishing | 1962 |
| A.D.T. Northumberland Limited | Other services | 1999 |
| A.J Lawn Financial Solutions Limited | Administrative & support | 2023 |
| A.R.T. Residential Developments Ltd | Real estate | 2021 |
| Abacus 449 Limited | Professional & scientific | 2004 |
| Abacus Children's Day Nursery Limited | Education | 2015 |
| ABC Childcare Limited | Real estate | 2002 |
| Abne Services Limited | Other services | 2016 |
| Abrinor Ltd | Wholesale & retail | 2015 |
| AC Fire Safety Ltd | Professional & scientific | 2009 |
| AC Tech Consultancy Ltd | Other services | 2011 |
| Accelerator Coaching Ltd | Administrative & support | 2020 |
| Acorn Landscapes (North East) Limited | Administrative & support | 2013 |
| Acorn Leisure Holidays Ltd | Hospitality | 2006 |
| Acorn Properties (Ncle) Limited | Real estate | 2013 |
| Acornford Holdings Ltd | Other services | 2017 |
| Active Future Northumberland CIC | Education | 2022 |
| AD Idem Properties Limited | Real estate | 2006 |
| Ad.Designsuk Ltd | Construction | 2025 |
| Adam Bell Building, Renovation & Maintenance Ltd | Construction | 2025 |
| Adam Rendell Ltd | Education | 2022 |
| Adapt Northumberland Ltd | Real estate | 2025 |
| Adelfi Property Holdings Ltd | Real estate | 2025 |
| Adet Advisory Ltd | Construction | 2025 |
| Admired Homes Limited | Real estate | 2019 |
| Advanced Lubricant Solutions Limited | Wholesale & retail | 2014 |
| ADVICE4BUSINESS North East Ltd | Administrative & support | 2013 |
| Aerauster Limited | Administrative & support | 2014 |
| Aesthetically SO Ltd | Health & social care | 2022 |
| AFV Modeller Limited | Information & communication | 2001 |
| Agbm Limited | Information & communication | 2012 |
| AIM North East Limited | Administrative & support | 2018 |
| Airbiotic Health and Wellness Research Limited | Administrative & support | 2013 |
| Alan Sankey Bricklaying & Stonemason Contractors Ltd | Construction | 2019 |
| Alan Stewart Limited | Construction | 2007 |
| Alan Thompson Builder Ltd | Construction | 2021 |
| Albert Fish Bar Ltd | Hospitality | 2024 |
| Albion Shield Ltd | Administrative & support | 2025 |
| Alcuin's School Ltd | Education | 2024 |
| Alderson Bookkeeping Ltd | Information & communication | 2022 |
| Alderson Law LLP | | 2004 |
| Alderton Vehicle Sales Ltd | Wholesale & retail | 2014 |
| Alfina Ltd | Professional & scientific | 2025 |
| Allan Bespoke Interiors Ltd | Construction | 2025 |
| Allan Building & Joinery Limited | Construction | 2006 |
| Allarch Properties Ltd | Real estate | 2025 |
| Allardice of Pitteuchar Limited | Real estate | 2025 |
| Allendale Properties Ltd | Real estate | 2021 |
| Alliance Fish Ltd | Agriculture & fishing | 2020 |
| Alnham Holdings Limited | Hospitality | 2018 |
| Alnorthumbria Property LLP | | 2009 |
| Alnwick Farmers Livestock Auction Company Limited | Agriculture & fishing | 1956 |
| Alnwick International Music Festival | Arts & recreation | 2000 |
| Alnwick Sporting Club Limited | Arts & recreation | 2007 |
| Alnwick Wizard Private Hire Ltd | Transport & logistics | 2023 |
| Alwinton Border Shepherds Show | Other services | 2018 |
| Alwinton Partership(The) | | 1987 |
| Amandalex Properties Limited | Real estate | 2024 |
| Amber Powervale Limited | Energy | 2020 |
| Amble Boat Company Limited | Manufacturing | 1995 |
| Amble Club,Limited(The) | Hospitality | 1902 |
| Amble Coastal Properties Limited | Hospitality | 2020 |
| Amble Development Trust | Other services | 1994 |