| Secure Management NE Ltd | Professional & scientific | 2013 |
| Secure Property Group Limited | Administrative & support | 2017 |
| Securemove Ltd. | Transport & logistics | 2014 |
| Secureshield Ltd | Administrative & support | 2019 |
| Securicorp (NE) Limited | Administrative & support | 2021 |
| SEE and Smile Ltd | Health & social care | 2021 |
| SEE Consultancy Services Ltd | Professional & scientific | 2025 |
| SEE ME Save ME Limited | Professional & scientific | 2016 |
| SEE Optical Company LLP | | 2009 |
| Seed Financial Solutions Ltd | Professional & scientific | 2024 |
| Seed Social North East C.I.C. | Agriculture & fishing | 2024 |
| Seeek Limited | Professional & scientific | 2021 |
| Seen and Heard Limited | Professional & scientific | 1977 |
| Segedunum Limited | Real estate | 2024 |
| Segedunum Sourcing Limited | Administrative & support | 2026 |
| Segero Ltd | Information & communication | 2013 |
| Seghill Trading Ltd | Wholesale & retail | 2021 |
| SEGHILL9 Limited | Information & communication | 2021 |
| Segmarg Ltd | Wholesale & retail | 2024 |
| Sehari Ltd | Hospitality | 2025 |
| Sehgal Commercial Properties Limited | Real estate | 1974 |
| Seimuuc Direct Services Limited | Construction | 2025 |
| Sekoala Holdings Ltd | Health & social care | 2015 |
| Sekura Window Centre Limited | Manufacturing | 2006 |
| Selara Capital Holdings Limited | Financial services | 2023 |
| Select Bars Ltd | Hospitality | 2017 |
| Select CS Ltd | Financial services | 2021 |
| Select Electrical Services (NE) Limited | Energy | 2016 |
| Select Information Systems Limited | Information & communication | 1994 |
| Select Living Limited | Construction | 2019 |
| Select Lofts & Builders Ltd | Construction | 2014 |
| Select Motors N.E Ltd | Wholesale & retail | 2016 |
| Select Property Developments Limited | Real estate | 2001 |
| Select Talent Group Ltd | Administrative & support | 2026 |
| Select Telecom Limited | Information & communication | 1997 |
| Select Telecom Networks Limited | Information & communication | 2008 |
| Selective Antibodies Limited | Professional & scientific | 1991 |
| Selekt Chicken (Newcastle) Ltd | Hospitality | 2025 |
| Self Detective Ltd | Health & social care | 2018 |
| Self Made Empire Ltd | Professional & scientific | 2018 |
| Seller DOT COM Ltd | Wholesale & retail | 2025 |
| Seller HR and Business Solutions Ltd | Professional & scientific | 2015 |
| Seller Morning Ltd | Information & communication | 2026 |
| Sellers Forged Ltd | Wholesale & retail | 2025 |
| Sellivate Ltd | Information & communication | 2022 |
| Sellmark Consulting Global Ltd | Wholesale & retail | 2024 |
| Sellmark Consulting LLP | | 2009 |
| Sellons 86 Limited | Information & communication | 1999 |
| Selltivate Ltd | Wholesale & retail | 2024 |
| Selto Properties Ltd | Real estate | 2016 |
| Sema London Ltd | Real estate | 2021 |
| Semch.Uk Construction Ltd | Construction | 2026 |
| Semper Excelsior Ltd | Transport & logistics | 2018 |
| Semphos Ltd | Manufacturing | 2019 |
| Semsmart Ltd | Professional & scientific | 2022 |
| SEN Trading Limited | Wholesale & retail | 2025 |
| Sena Property Management Ltd | Real estate | 2025 |
| Senate Engineering Ltd | Professional & scientific | 2020 |
| Send IT Events Limited | Arts & recreation | 2017 |
| Senda Aurea Limited | Wholesale & retail | 2025 |
| Sengupta Medical Limited | Health & social care | 2016 |
| Senjd Ltd | Real estate | 2024 |
| Senn Holdings Ltd | Financial services | 2022 |
| Sennections Ltd | Administrative & support | 2026 |
| Sensecheck Technologies Limited | Information & communication | 2020 |
| Senserve Limited | Other services | 2013 |
| Senshealth Ltd | Health & social care | 2021 |
| Sensilium Limited | Information & communication | 2024 |
| SENSING360 Ltd | Professional & scientific | 2025 |
| Sensinom Ltd | Administrative & support | 2019 |
| Sensisupport Ltd | Health & social care | 2026 |
| Sentinel Energy Limited | Energy | 2016 |
| Sentio AI Limited | Information & communication | 2025 |
| Sephico Ltd | Information & communication | 2026 |
| Sepi 2 Ltd | Construction | 2024 |
| Sepi Ltd | Real estate | 2023 |
| Septa Design Limited | Construction | 2025 |
| September Three Limited | Extraterritorial | 2014 |
| Sequoia Property Holdings Ltd | Real estate | 2021 |
| Seraa LMT Limited | Construction | 2025 |
| Seraphina Symbol Design Ltd | Professional & scientific | 2026 |
| Serendib Group International Ltd | Wholesale & retail | 2023 |
| Serendipity Training Ltd | Education | 2011 |
| Serenelet Properties Ltd | Real estate | 2024 |
| Serenitiscan LLP | | 2025 |
| Serenity Counselling Services Ltd | Health & social care | 2026 |
| Serenity Homes NE Ltd | Real estate | 2025 |
| Serenity Spa & Skincare Limited | Other services | 2023 |
| Serenus Developments Limited | Construction | 2017 |
| Sergio Antequera Logistics Ltd | Transport & logistics | 2025 |
| Seriento Limited | Real estate | 2021 |
| Serios Group Limited | Information & communication | 2020 |
| Serious About Safety Limited | Other services | 2006 |
| Sernero Advertising Ltd | Administrative & support | 2020 |
| Serovella London Ltd | Wholesale & retail | 2026 |
| SERTUR2024 Ltd | Professional & scientific | 2024 |
| Servbet Limited | Real estate | 1999 |
| Service & Disabled Lifts Ltd | Construction | 2015 |
| Service & Maintenance Bureau Ltd | Construction | 2024 |
| Service Integration & Operations Ltd | Professional & scientific | 2018 |