| Search 4 Furniture Limited | Wholesale & retail | 2017 |
| Searchlight Magazine Limited | Information & communication | 1990 |
| Seaview Traders Limited | Other services | 2022 |
| SEB & Rebe Taxis Ltd | Transport & logistics | 2024 |
| SEB Invest Ltd | Construction | 2024 |
| SEB Mobile Auto Mechanic Ltd | Wholesale & retail | 2022 |
| SEB Servicing Limited | Construction | 2026 |
| Sebasell Ltd | Wholesale & retail | 2012 |
| Sebastian Film Ltd | Information & communication | 2022 |
| Sebco Creative Limited | Administrative & support | 2013 |
| Sebex Investments Ltd | Information & communication | 2017 |
| Sebreez Track Ltd | Wholesale & retail | 2020 |
| Secant Technologics Ltd | Information & communication | 2024 |
| Second Gulliver Properties Group | | 1966 |
| Second LAP Ltd | Information & communication | 2024 |
| Second Roots Ltd | Health & social care | 2026 |
| Second Site Limited | Manufacturing | 2022 |
| Second Slice Ltd | Hospitality | 2025 |
| Secore Biotech Limited | Professional & scientific | 2026 |
| Secret Brand Helpers Ltd | Wholesale & retail | 2024 |
| Secret Gardens London Ltd | Hospitality | 2019 |
| Secrets of Motivation Ltd | Health & social care | 2025 |
| Secta Construction Limited | Construction | 2019 |
| Sectorguard Services Ltd | Administrative & support | 2024 |
| Securashine Ltd | Administrative & support | 2025 |
| Securcorp Ltd | Financial services | 2026 |
| Secure Brain Solutions Limited | Real estate | 2017 |
| Secure Briton K9 Ltd | Administrative & support | 2024 |
| Secure Care London Ltd | Health & social care | 2023 |
| Secure Essex Ltd | Administrative & support | 2023 |
| Secure Fire Doors Ltd | Construction | 2020 |
| Secure Management Services Ltd | Administrative & support | 2017 |
| Secure Protection London Limited | Administrative & support | 2015 |
| Secure Serve Ltd | Administrative & support | 2022 |
| Secure Skills Learning Limited | Health & social care | 2023 |
| Secure Trading Limited | Other services | 2022 |
| SECURE1ST and Facilities Management Ltd | Administrative & support | 2023 |
| Securecare (UK) Limited | Administrative & support | 2007 |
| Secured Service Global Ltd | Financial services | 2024 |
| Secureit K9 Limited | Administrative & support | 2024 |
| Secureline Security Services Ltd | Administrative & support | 2024 |
| Securelogix Ltd | Information & communication | 2018 |
| Securepath Solutions Ltd | Wholesale & retail | 2023 |
| Securepoint Services Ltd | Administrative & support | 2026 |
| Securesphere Security Services Limited | Wholesale & retail | 2025 |
| Securetech Solutions Limited | Administrative & support | 2006 |
| Securitel Ltd | Information & communication | 2026 |
| Securiton Services Limited | Professional & scientific | 2014 |
| Security 123 Ltd | Administrative & support | 2025 |
| Security 1234 Ltd | Administrative & support | 2025 |
| Security 12345 Ltd | Administrative & support | 2025 |
| Security Crew Ltd. | Administrative & support | 2021 |
| Security Earpiece Ltd | Wholesale & retail | 2022 |
| Security Fire Doors Ltd | Construction | 2020 |
| Security Guards 247 Ltd | Administrative & support | 2018 |
| Security Industry Services Ltd | Administrative & support | 2017 |
| Security SOLUTIONS4U (UK) Ltd | Information & communication | 2014 |
| Securivas Ltd | Professional & scientific | 2019 |
| Sedpaac Ltd | Wholesale & retail | 2022 |
| SEE Rail PLC | Construction | 2016 |
| SEE Services Ltd | Construction | 2014 |
| Seed of Light Basildon Limited | Health & social care | 2025 |
| Seed of Light Group Ltd | Professional & scientific | 2025 |
| Seed of Light Ltd | Health & social care | 2023 |
| Seegold Ltd | Wholesale & retail | 2025 |
| Seek the Light Ltd | Professional & scientific | 2025 |
| Seekoni Consulting Limited | Professional & scientific | 2022 |
| Seema London Ltd | Wholesale & retail | 2021 |
| Seetha Cranbrook Ltd | Real estate | 2025 |
| Seetha Creations Ltd | Real estate | 2020 |
| Seetha Group Limited | Real estate | 2013 |
| Seetha London Limited | Construction | 2013 |
| Seetha Management Ltd | Real estate | 2020 |
| Seetha Properties Ltd | Real estate | 2018 |
| Seevz Ltd | Construction | 2025 |
| Seezan Ltd | Wholesale & retail | 2025 |
| Sega Work Ltd | Professional & scientific | 2025 |
| Segadel Investments Ltd | Real estate | 2020 |
| Sehgal Cars Ltd | Transport & logistics | 2022 |
| Seifemichael Ltd. | Construction | 2016 |
| Seine Cottage Ltd | Real estate | 2025 |
| Seizethemoment.Uk Ltd | Professional & scientific | 2026 |
| Sekana Medicolegal Ltd | Information & communication | 2026 |
| Selaxy Ltd | Wholesale & retail | 2025 |
| Selbone Limited | Wholesale & retail | 2018 |
| Selborne Road Ltd | Real estate | 2021 |
| Select Brands Ltd | Wholesale & retail | 2018 |
| Select Facilities Services Ltd | Other services | 2014 |
| Select Land Developments Ltd | Real estate | 2005 |
| Select Right Properties Limited | Construction | 2017 |
| Select Source Ltd | Professional & scientific | 2019 |
| Select UK Recruitment Ltd | Administrative & support | 2021 |
| Selectum Ltd | Administrative & support | 2024 |
| Self Studyuk Ltd | Administrative & support | 2022 |
| Self-Ish Space Ltd | Arts & recreation | 2025 |
| Selfconstruct Ltd | Construction | 2022 |
| Selim Consultancy Ltd | Information & communication | 2024 |
| Selina Manir Finance Ltd | Financial services | 2022 |
| Selina Property Ltd | Real estate | 2019 |
| Selkirk Colyers Limited | Information & communication | 2023 |