| Salon NO 5 Limited | Other services | 2013 |
| Salt & Tides Ltd | Hospitality | 2026 |
| Salus Avenya Ltd | Health & social care | 2016 |
| Sambuca Morpeth Ltd | Hospitality | 2025 |
| Sampson Civil Engineering Ltd | Construction | 2025 |
| Samuel James Properties Ltd | Real estate | 2019 |
| Sandco 906 Limited | Administrative & support | 2005 |
| Sanders & Cooper Estates Limited | Hospitality | 2016 |
| Sanders Estates NE Limited | Real estate | 2020 |
| Sanders Group (NE) Limited | Financial services | 2019 |
| Sandersons Plumbing & Heating Ltd | Construction | 2026 |
| Sandpiper Farms Limited | Agriculture & fishing | 1995 |
| Sankey Construction (NE) Ltd | Construction | 2025 |
| Sansoms Specialist Cars Limited | Wholesale & retail | 2022 |
| Santiago 21 Limited | Real estate | 2024 |
| Sara Anton Limited | Other services | 2007 |
| Sarah ANN Homes Ltd | Real estate | 2022 |
| Sarah Gilmour Aesthetics Limited | Health & social care | 2020 |
| Sarah Walden Photography Ltd. | Professional & scientific | 2019 |
| Sars Trading Ltd | Hospitality | 2017 |
| Saunderson Limited | Real estate | 2018 |
| SAVI3M Tech UK Ltd | Professional & scientific | 2025 |
| Sawyer Developments Limited | Real estate | 2016 |
| SC2 Ltd | Real estate | 2012 |
| Scenic Photos Limited | Professional & scientific | 2003 |
| Scott BIM Services Ltd | Construction | 2007 |
| Scott Energy Services Limited | Administrative & support | 2015 |
| Scott Investments (North East) Limited | Professional & scientific | 2018 |
| Scottmech Offshore Ltd. | Mining & quarrying | 2013 |
| Scrub in Limited | Information & communication | 2025 |
| SDS Marine Engineering Services Ltd | Manufacturing | 2016 |
| Sea View (Longframlington) Management Company Limited | Real estate | 2020 |
| SEA2ELECTRICITY Ltd | Energy | 2022 |
| Seareach Management Services Limited | Professional & scientific | 2017 |
| Seaside Joinery Ltd | Construction | 2021 |
| Seawaves Studio Ltd | Manufacturing | 2017 |
| Seeva Media Ltd | Professional & scientific | 2024 |
| Semantic Space Limited | Information & communication | 2025 |
| Sensei Training & Development Ltd | Professional & scientific | 2014 |
| Senselogic Ltd | Information & communication | 2025 |
| Serene Short Stays Ltd | Real estate | 2022 |
| Serene Urban Living Ltd | Real estate | 2025 |
| Serenity-By-The-Sea Northumberland Limited | Arts & recreation | 2026 |
| Serve-North GAS Plumbing & Heating Ltd | Construction | 2020 |
| Service Concepts Ltd | Administrative & support | 2025 |
| SFT2009 Limited | Professional & scientific | 2009 |
| SFT2009 NO.2 Limited | Professional & scientific | 2009 |
| SGC Estates Ltd | Real estate | 2024 |
| Sharp Growth Limited | Professional & scientific | 2025 |
| Sharp Professional Cleaning Co Ltd | Administrative & support | 2025 |
| Shaun Brown Builders Limited | Construction | 2023 |
| Shelgo Tea Ltd | Wholesale & retail | 2018 |
| Sheona Della-Fort Wellbeing Coaching CIC | Professional & scientific | 2024 |
| Shepherd Investments Ltd | Real estate | 2025 |
| Shepherds Retreats Ltd | Hospitality | 2018 |
| Shepherds Walks Limited | Wholesale & retail | 2015 |
| Shield Green Trading Company Ltd | Manufacturing | 2017 |
| Shiney Stones Developments Limited | Real estate | 2006 |
| Shinobi Ltd. | Information & communication | 2000 |
| Shire Capital Ltd | Professional & scientific | 2009 |
| Shopjacket Limited | Administrative & support | 2010 |
| Shotgunchewy Limited | Health & social care | 2019 |
| SHP Networks Ltd | Information & communication | 2023 |
| Shsc Limited | Information & communication | 2019 |
| SIA Education Ltd | Education | 2016 |
| Siat Properties Limited | Real estate | 2016 |
| Siella Beauty Limited | Other services | 2026 |
| Silverfoxx Limited | Health & social care | 2025 |
| Silverhills Garden Centre Ltd | Real estate | 1990 |
| Simonside Engineering Limited | Professional & scientific | 2019 |
| Simonside Marketing Ltd | Professional & scientific | 2019 |
| Simple Focus Limited | Transport & logistics | 2021 |
| Simpli Projects Limited | Professional & scientific | 2015 |
| Simulacra Enterprises Ltd | Information & communication | 2015 |
| Sincera Retail Solutions Ltd | Administrative & support | 2018 |
| Sinclair Irvine Limited | Professional & scientific | 2021 |
| Singh & Sons Ltd | Wholesale & retail | 2006 |
| Site Maintenance Limited | Other services | 2006 |
| Site Staff Limited | Administrative & support | 2013 |
| Site Staff Recruitment Limited | Administrative & support | 2013 |
| SIX Design and Build Ltd | Construction | 2021 |
| SJH Management Ltd | Households | 2026 |
| SJK Architectural Services Ltd | Administrative & support | 2017 |
| SJS Analysis Ltd | Real estate | 2020 |
| SJS One Ltd | Wholesale & retail | 2021 |
| SJT70 Ltd | Transport & logistics | 2016 |
| Skanderbeg Finance Ltd | Professional & scientific | 2023 |
| Sketch Book Design Ltd | Other services | 2013 |
| Sky Datacomms Ltd | Construction | 2003 |
| Skylark Finance Group Ltd | Financial services | 2023 |
| Skyline Commercial Property Limited | Financial services | 2021 |
| Skyline Durham Holdco Limited | Financial services | 2019 |
| Skyline Durham Limited | Real estate | 2013 |
| Skyline Residential Property Limited | Real estate | 2022 |
| Slemany Company Limited | Other services | 2015 |
| Slickshoot Limited | Information & communication | 2011 |
| Sljh Limited | Construction | 2016 |
| Slotchase Property Management Limited | Households | 1989 |
| Smart Global Services Ltd | Administrative & support | 2017 |
| Smarter Hybrid Ltd | Other services | 2025 |