| Skelton Scaffolding Ltd | Construction | 2020 |
| Skewjack 71 Limited | Real estate | 1957 |
| Skilled Systems Ltd | Professional & scientific | 2010 |
| Skillora Sports Ltd | Information & communication | 2025 |
| Skillorbit Ltd | Wholesale & retail | 2025 |
| Skills for People | Health & social care | 1997 |
| Skillsplay Ltd | Information & communication | 2021 |
| Skin & Medical Aesthetics by Sally Ltd | Health & social care | 2025 |
| Skin & Soul Education Ltd | Other services | 2024 |
| Skin & Soul Medical Ltd | Other services | 2021 |
| Skin Clinic & Permanent Makeup Academy Ltd | Other services | 2020 |
| Skin Darras Hall Ltd | Other services | 2024 |
| Skin LAB Aesthetics by DR Shaymaa Ltd | Other services | 2025 |
| Skin LAB Aesthetics Training Academy Ltd | Education | 2026 |
| Skin Life Analytics Limited | Professional & scientific | 2022 |
| Skin Vitality Medical Aesthetics Ltd | Health & social care | 2019 |
| Skinbiotherapeutics PLC | Health & social care | 2015 |
| Skinbiotix Limited | Health & social care | 2017 |
| Skinfinity Medical Aesthetics Ltd | Other services | 2020 |
| Skingossips Ltd | Wholesale & retail | 2024 |
| Skinology Skin Therapy Limited | Other services | 2020 |
| Skinpoint Aesthetics Ltd | Health & social care | 2025 |
| Skivers Ltd | Wholesale & retail | 2026 |
| Skratch Enterprises Limited | Construction | 2004 |
| SKS Consulting Limited | Professional & scientific | 2004 |
| Skull Club Graphic Solutions Ltd | Manufacturing | 2024 |
| Skullen Collective Ltd | Other services | 2019 |
| Skullen Commune Ltd | Other services | 2023 |
| Sky High Global Limited | Real estate | 2023 |
| Sky Smart Limited | Wholesale & retail | 2023 |
| Sky View Consultancy Ltd | Professional & scientific | 2025 |
| Skybuddy Ltd | Professional & scientific | 2023 |
| Skye Developments NE Ltd | Real estate | 2019 |
| Skye Lettings Ltd | Real estate | 2021 |
| Skye Marine Engineering Ltd | Manufacturing | 2024 |
| Skye Medical Limited | Health & social care | 2019 |
| Skyimage Limited | Professional & scientific | 2014 |
| Skyjoin Property Management Limited | Households | 1991 |
| Skylicious Limited | Hospitality | 2018 |
| Skylift Newcastle Limited | Construction | 2019 |
| Skyline Accomodations Ltd | Real estate | 2024 |
| Skyline Garden Limited | Hospitality | 2024 |
| Skyline Tiling Ltd | Construction | 2018 |
| Skyline UK Contracts Limited | Professional & scientific | 2016 |
| Skymash Solutions Ltd | Information & communication | 2025 |
| Skyrex Services Limited | Other services | 2010 |
| Skys Property NE Ltd | Real estate | 2015 |
| Skytuch Limited | Wholesale & retail | 2009 |
| Skywin Global Consultancy Limited | Professional & scientific | 2025 |
| SL Mini Market Limited | Wholesale & retail | 2018 |
| SL Pressure Washing Ltd | Administrative & support | 2025 |
| SL Shek Limited | Real estate | 2017 |
| Slack's CIC | Information & communication | 2024 |
| Slade Properties (NE) Limited | Extraterritorial | 2022 |
| Slade Roofing Contractors Limited | Construction | 1998 |
| Slamfresh CIC | Education | 2018 |
| Slap League UK Ltd | Information & communication | 2025 |
| Slater and Wood Ltd | Professional & scientific | 2022 |
| Slater Drive Systems Limited | Extraterritorial | 2008 |
| Slater Jackson Associates Limited | Construction | 2001 |
| Slattery Holdings Ltd | Information & communication | 2024 |
| Slatyford Local Ltd | Wholesale & retail | 2023 |
| Slave to the Rave Ltd | Wholesale & retail | 2020 |
| SLB Solutions NE Ltd | Construction | 2026 |
| SLC Project Management Limited | Construction | 2016 |
| Sleekr Autocare Ltd | Manufacturing | 2025 |
| Sleep Research and Consulting Limited | Professional & scientific | 2015 |
| Sleepwell (Cumbria) Limited | Hospitality | 2017 |
| Sleets Realisations Limited | | 1944 |
| SLF Advisory Ltd | Professional & scientific | 2025 |
| SLG Makeup and Lashes Ltd | Other services | 2018 |
| Slideart CUT Unisex Salon Limited | Other services | 2025 |
| SLJ Inspections Ltd | Professional & scientific | 2014 |
| SLJ Safety Services Limited | Professional & scientific | 2025 |
| SLM Brickwork NE Ltd | Construction | 2026 |
| Slmp Limited | Administrative & support | 2022 |
| Sloakee Ltd | Information & communication | 2026 |
| Sloobie Ltd | Wholesale & retail | 2022 |
| Sloppy Grill Limited | Hospitality | 2024 |
| Slot-Streamers Ltd | Professional & scientific | 2021 |
| Slow Shopping Ltd | Health & social care | 2016 |
| SLS Aero Limited | Transport & logistics | 2024 |
| Slsl Associates Ltd. | Wholesale & retail | 2021 |
| Slugtown CIC | Arts & recreation | 2019 |
| SM Consulting PVT Limited | Health & social care | 2023 |
| SM Farms Limited | Agriculture & fishing | 1998 |
| SM Law | Administrative & support | 2010 |
| SM Properties North East Limited | Real estate | 2023 |
| SM Recruitment Solutions Limited | Administrative & support | 2024 |
| Smah Group Ltd | Real estate | 2020 |
| Smajo Beso Consulting Ltd | Professional & scientific | 2026 |
| Small Bytes Ltd | Information & communication | 2025 |
| Small Plant & Garden Machinery Spares Ltd | Wholesale & retail | 2014 |
| Smallspark Space Systems Limited | Professional & scientific | 2018 |
| Smart Buildings Limited | Construction | 2012 |
| Smart Dogs Training Ltd | Agriculture & fishing | 2020 |
| Smart Factory Rise Limited | Information & communication | 2025 |
| Smart Fitness Gyms Limited | Arts & recreation | 2010 |
| Smart Logistics NE Ltd. | Financial services | 2019 |
| Smart Multi Academy Trust | Education | 2016 |