| Simply Optimised Limited | Professional & scientific | 2025 |
| Simply Properties Teesside Limited | Real estate | 2017 |
| Simpson Tech Services Ltd | Manufacturing | 2013 |
| Sindy Ltd | Wholesale & retail | 2022 |
| Sing Tea Limited | Manufacturing | 2025 |
| Singapore Titan.Ai Ltd | Information & communication | 2025 |
| Sinstead Automation Ltd | Professional & scientific | 2017 |
| SIP N SIP Ltd | Wholesale & retail | 2022 |
| Sirius (NE) Limited | Transport & logistics | 2012 |
| Sirplantalot Productions Ltd | Professional & scientific | 2023 |
| Sirse Limited | Administrative & support | 2015 |
| Sirus Consulting Ltd | Professional & scientific | 2017 |
| Sisco Capital Assets Ltd | Financial services | 2016 |
| Sistex Limited | Wholesale & retail | 2013 |
| Sistine Properties (Suffolk) Limited | Construction | 2025 |
| Sistine Properties (Thetford) Limited | Real estate | 2008 |
| Sistine Properties Limited | Real estate | 2007 |
| Sitaara Properties Ltd | Real estate | 2022 |
| Sitesee Safety Limited | Professional & scientific | 2024 |
| SIX Commercial Cleaning Limited | Administrative & support | 2025 |
| SIX Group Holdings Limited | Financial services | 2025 |
| SIX Linen Limited | Wholesale & retail | 2025 |
| SJ MC Ltd | Construction | 2019 |
| SJ Resources Limited | Professional & scientific | 2015 |
| SJA Inspection Ltd | Professional & scientific | 2019 |
| SJC Comms (NE) Ltd | Construction | 2023 |
| SJC Engineering Design Ltd | Professional & scientific | 2016 |
| Sjkg Inst. Ltd | Manufacturing | 2026 |
| SJM Automation Ltd | Professional & scientific | 2022 |
| SJR Assets Limited | Professional & scientific | 2023 |
| SJR Electrical Services Ltd | Construction | 2024 |
| SK AI Solutions Ltd | Information & communication | 2025 |
| SK Estate and Lettings Ltd | Real estate | 2020 |
| SK Leisure Park Limited | Real estate | 2023 |
| SK Sports and Education Limited | Arts & recreation | 2017 |
| SK Vapes Ltd | Wholesale & retail | 2023 |
| SKD Holdings Limited | Real estate | 2022 |
| Skdproperty Ltd | Real estate | 2023 |
| SKF Engineering Ltd | Professional & scientific | 2025 |
| SKG Trading Northeast Ltd | Wholesale & retail | 2025 |
| Skills Barber's (NE) Ltd | Other services | 2022 |
| Skinology-Uk Ltd | Wholesale & retail | 2025 |
| Skinvestment NE Ltd | Other services | 2026 |
| Skoda Land Limited | Wholesale & retail | 2012 |
| Skralls Ltd | Information & communication | 2025 |
| Skutterskelfe Anglers Limited | Agriculture & fishing | 1984 |
| Sky Deck Clothing Limited | Wholesale & retail | 2024 |
| Sky Water Bar & Restaurants Ltd | Hospitality | 2022 |
| Skylite Logistics Limited | Transport & logistics | 2024 |
| Skyrim Global Limited | Manufacturing | 2025 |
| Skyscaner Travel & Tours Limited | Administrative & support | 2025 |
| SL (NE) Ltd | Construction | 2020 |
| SL Locums Ltd | Health & social care | 2023 |
| SL Plant Operators Ltd | Construction | 2016 |
| Slap Dash Decorating Limited | Other services | 2025 |
| Slater Refrigeration Ltd | Manufacturing | 2007 |
| Slavic Boro Ltd | Wholesale & retail | 2025 |
| Slb-Eng Ltd | Professional & scientific | 2024 |
| SLC Complete Ltd | Financial services | 2018 |
| SLC Hseq Ltd | Professional & scientific | 2025 |
| Sleepy Hollow Planning Limited | Professional & scientific | 2008 |
| Sleepy-O Ltd | Manufacturing | 2023 |
| Slemani Restaurant NE Ltd | Hospitality | 2020 |
| SLF Scaffolding Ltd | Construction | 2026 |
| SLI Offshore & Logistics Limited | Transport & logistics | 2026 |
| SLJ Telecoms Limited | Information & communication | 2009 |
| SLS Management Services Ltd | Professional & scientific | 2021 |
| SLT Wellness Ltd | Other services | 2024 |
| Slud Ltd | Manufacturing | 2015 |
| SLV CON Ltd | Construction | 2025 |
| SLW Engineering Limited | Construction | 2022 |
| SLW Mortgages Ltd | Financial services | 2020 |
| SM Consultancy (NE) Limited | Financial services | 2019 |
| SM Consultancy Services North East Limited | Professional & scientific | 2018 |
| SM Digital Solutions Ltd | Information & communication | 2025 |
| SM Ecom Solutions Ltd | Wholesale & retail | 2025 |
| SM Hasan Trading Ltd | Wholesale & retail | 2025 |
| Sm.Hl Consultant Ltd | Professional & scientific | 2025 |
| Small Access Limited | Construction | 2012 |
| Smart Call AI Limited | Information & communication | 2025 |
| Smart Constructors Ltd | Construction | 2025 |
| Smart Living Properties Ltd | Real estate | 2018 |
| Smart Mini Market (NE) Ltd | Wholesale & retail | 2025 |
| Smart Projects and Solutions Ltd | Professional & scientific | 2017 |
| Smart Solutions Inc Ltd | Professional & scientific | 2023 |
| Smartfix Boro Limited | Manufacturing | 2025 |
| SMARTGADJETS4U Ltd | Other services | 2023 |
| Smash & Scoops Limited | Hospitality | 2025 |
| Smash IT Group Ltd | Hospitality | 2025 |
| SMC Holdings Teesside Limited | Financial services | 2022 |
| SMC Properties(Ne) Ltd | Real estate | 2022 |
| SME Centre of Excellence (Cofe) Tees Valley (Smetv) Limited | Hospitality | 2020 |
| Smesh Burger Limited | Hospitality | 2025 |
| Smethwick Practice Limited | Health & social care | 2018 |
| SMG Electrical Engineering Ltd | Construction | 2023 |
| Smith & Co Renewable Energy Ltd | Construction | 2026 |
| Smith Bro's Contractors Ltd | Other services | 2025 |
| Smith P a Limited | Wholesale & retail | 2008 |
| Smithers Group Limited | Wholesale & retail | 2024 |
| Smithfield Timber Limited | Wholesale & retail | 1990 |