| Scholars Park (Moorside) Management Company Limited | Households | 2026 |
| Scott Mitchell Veterinary Care Limited | Professional & scientific | 2020 |
| Scotts of Alnwick Limited | Wholesale & retail | 2002 |
| Seaton Pharma Group Limited | Wholesale & retail | 2024 |
| Secrets Salon Limited | Other services | 2003 |
| Shape House Health Club Limited | Arts & recreation | 2004 |
| Shiellow Wood Limited | Agriculture & fishing | 2006 |
| Simon Fraser Photography Limited | Professional & scientific | 2002 |
| SIU and Tsang Company Limited | Hospitality | 2003 |
| Siu's Company Limited | Hospitality | 2003 |
| Smailes & Hannant Limited | Construction | 2003 |
| Smeal Consulting Limited | Professional & scientific | 2004 |
| Softrite Ltd | Information & communication | 1997 |
| Southernwood Property Limited | Real estate | 2006 |
| Spar Wylam Limited | Administrative & support | 2003 |
| Specialist Global Sourcing Ltd | Administrative & support | 2009 |
| Speedway Taxis | | 1987 |
| Spine Biotech Limited | Manufacturing | 1998 |
| Ssdos Limited | Financial services | 2009 |
| Stalwick Limited | Administrative & support | 1987 |
| Standing Stone Drawing Office Supplies Limited | Wholesale & retail | 2004 |
| Standol Ltd | Professional & scientific | 2007 |
| Standwell Furniture Limited | Manufacturing | 2025 |
| Stanley Power Tools Limited | | 1941 |
| Stanners Equipment Limited | Wholesale & retail | 1980 |
| Stannington Estates Limited | Real estate | 2003 |
| Stanton Partners | | 1996 |
| Stembridge Solicitors Limited | Professional & scientific | 2007 |
| Stephenson Armstrong Consultants Limited | Professional & scientific | 1978 |
| Steven Pridmore Limited | Construction | 2023 |
| Storey & SON (Builders) Limited | Construction | 2024 |
| Strands (Amble) Limited | Other services | 2003 |
| Strathearn Leisure Parks Limited | Administrative & support | 1959 |
| Straughan Investments Limited | Professional & scientific | 2016 |
| Stuart Duffield Electrical Ltd | Construction | 2023 |
| Summerson Place (Darlington) Phase 1 Management Company Limited | Households | 2021 |
| Summerson Place (Darlington) Phases 2 and 3 Management Company Limited | Households | 2024 |
| Sureclad UK Limited | Wholesale & retail | 2006 |
| Sw.Ws Limited | Construction | 2006 |
| Swallow Fish Limited | Hospitality | 1980 |
| Swarland Technical Limited | Information & communication | 2001 |
| Sycamore Place (Barrasford) Management Company Limited | Households | 2025 |
| T James Storage Limited | Transport & logistics | 2018 |
| T.James(Bedlington),Limited | Transport & logistics | 1965 |
| Tallantyre Design Limited | Professional & scientific | 1986 |
| Tallantyre Gallery Limited | Wholesale & retail | 2004 |
| Tallantyre Wallcoverings Limited | Wholesale & retail | 1978 |
| Taylor Structural Engineers Ltd | Construction | 2007 |
| TD Locum Services Limited | Wholesale & retail | 2008 |
| Techflow Marine (Flexibles) Ltd | Manufacturing | 2023 |
| Techflow Marine (Ports & Terminals) Ltd | Manufacturing | 2023 |
| Techflow Marine Holdings Ltd | Financial services | 2023 |
| TED Developments Ltd | Other services | 2007 |
| Telemetry-Online Limited | Manufacturing | 2003 |
| TG365 Recruitment Limited | Administrative & support | 2026 |
| Thatch 2 Ltd | Other services | 2006 |
| THE Big Green Building Company Ltd | Construction | 2010 |
| THE Coquet Valley Kitchen Company Limited | Manufacturing | 2026 |
| THE Divan Clan Limited | Manufacturing | 2018 |
| THE Dock Hotel Limited | Hospitality | 2005 |
| THE Fold Farm (Holding Company) Limited | Financial services | 2022 |
| THE Garage Customs and Classics Limited | Wholesale & retail | 2023 |
| THE Great Northern Apothecary Co. Limited | Manufacturing | 2006 |
| THE Housesteads Group Ltd | Professional & scientific | 2024 |
| THE Origin Beer Company Ltd | Manufacturing | 2019 |
| THE Repro Centre Limited | Wholesale & retail | 2005 |
| THE Three Little W'S Limited | Professional & scientific | 2003 |
| THE Village Veterinary Centre Limited | Professional & scientific | 2006 |
| THE Whitehouse Centre Ltd | Arts & recreation | 1970 |
| Thompson Group Calibration Limited | Administrative & support | 2018 |
| Thompson Group Heavy Transport Limited | Extraterritorial | 2018 |
| Thompson Group Industrial Tooling Limited | Manufacturing | 2025 |
| Thompson Group Offshore Limited | Administrative & support | 2018 |
| Thompson Industrial Group Holdings Limited | Financial services | 2017 |
| Thornton Brothers Limited | Wholesale & retail | 1996 |
| Tofco CPP Limited | Manufacturing | 2006 |
| Toft's (Confectioners) Limited | | 1963 |
| Transcend (Hair and Beauty) Limited | Other services | 1999 |
| Transped Limited | Transport & logistics | 1997 |
| Trees Please (Holdings) Limited | Financial services | 2026 |
| Trekko Sports Limited | Professional & scientific | 1981 |
| Troynorth Limited | Wholesale & retail | 1977 |
| Tulip Holdings N E Ltd | Construction | 2023 |
| Tulip Interiors N E Ltd | Professional & scientific | 2022 |
| Tulip Marine Ltd | Agriculture & fishing | 2023 |
| Tustain Motors Holdings Limited | Financial services | 2025 |
| Tweed Salmon Centre CIC | Arts & recreation | 2023 |
| Tyne Mills Motor Company Limited | Real estate | 1986 |
| Tyne Vale Financial Services Limited | Financial services | 1987 |
| Tyne Valley Tyres Limited | Real estate | 1985 |
| Tynedale Boiler Maintenance Ltd | Construction | 2007 |
| Underwood Hall Limited | Health & social care | 1996 |
| Usatco Europe Limited | Wholesale & retail | 2026 |
| V Salon Tanning Limited | Other services | 2007 |
| Vapestreams Limited | Wholesale & retail | 2017 |
| Vision Developments Limited | Construction | 1992 |
| Voialthem Ltd | Administrative & support | 2021 |
| W & P Roofing Services Ltd | Construction | 2019 |
| W a Lawrence (Fishing) Limited | Agriculture & fishing | 2003 |
| W. L. Straughan & SON Limited | Administrative & support | 2002 |