| Secureicemk Ltd | Wholesale & retail | 2019 |
| Securevirtual Holdings Limited | Financial services | 2012 |
| Securitas Security Services (UK) Limited | Administrative & support | 1973 |
| Securitas Security Services Ltd | Extraterritorial | 1991 |
| Securitas Services Holding UK Limited | Professional & scientific | 2006 |
| Securitas Technology Limited | Manufacturing | 1922 |
| Securitas Transport Aviation Security (UK) Limited | Administrative & support | 2009 |
| Security Combat Solutions Ltd | Administrative & support | 2025 |
| Security Kings Limited | Administrative & support | 2015 |
| Securvote Ltd | Other services | 2024 |
| Sedek Limited | Information & communication | 2007 |
| Sedem Express Limited | Health & social care | 2012 |
| Sedition Recordings Limited | Other services | 1984 |
| Sedra Limited | Real estate | 2016 |
| SEE Light Trading Ltd | Wholesale & retail | 2020 |
| SEE Through Stories Ltd | Information & communication | 2021 |
| Seebeck 129 Limited | Real estate | 2015 |
| Seed 247 H.C. Consultants Limited | Professional & scientific | 2018 |
| Seed Forum International Foundation | Extraterritorial | 2004 |
| Seed Global Limited | Information & communication | 2017 |
| Seed Property Holdings Ltd | Real estate | 2017 |
| Seed Property Investment Ltd | Real estate | 2020 |
| Seedos Ltd. | Wholesale & retail | 1998 |
| Seedtech Systems Ltd | Other services | 2024 |
| Seek the Peaks Limited | Information & communication | 2009 |
| Seekhana Limited | Information & communication | 2016 |
| Seekwell Service Ltd | Information & communication | 2014 |
| Seema Infosystems Ltd | Information & communication | 2023 |
| Seequal Software PVT Limited | Information & communication | 2008 |
| Seferi Construction Ltd | Construction | 2013 |
| SEG Global Limited | Water & waste | 2026 |
| Segan Homes (UK) Limited | Real estate | 2024 |
| Segmot Consulting Limited | Professional & scientific | 2018 |
| Segremplus Ltd | Professional & scientific | 2020 |
| Seismic Software UK Limited | Information & communication | 2017 |
| Seitai Limited | Health & social care | 2001 |
| Seka Property Ltd | Real estate | 2025 |
| Seko City Ltd | Wholesale & retail | 2016 |
| Seko Properties Ltd | Real estate | 2025 |
| Selandme Limited | Financial services | 2017 |
| Select Estate Property & Real Estate Limited | Real estate | 2014 |
| Select Homes (MK) Ltd | Real estate | 2017 |
| Select Social Care Ltd | Health & social care | 2018 |
| Selectline Solutions Ltd | Administrative & support | 2016 |
| Seleous Ltd | Hospitality | 2020 |
| Self Control Media Limited | Professional & scientific | 2025 |
| Self Enrolment National Self Exclusion Ltd | Administrative & support | 2022 |
| Selfie Factory Ltd | Arts & recreation | 2018 |
| Selftrek Ltd | Wholesale & retail | 2025 |
| Selhome Limited | Real estate | 2021 |
| Selina Ocean Ltd | Professional & scientific | 2021 |
| Seljo Ltd | Wholesale & retail | 2025 |
| Sell More Pizza Limited | Hospitality | 2017 |
| Sell Surplus IT Ltd | Information & communication | 2022 |
| Sells Consultancy Limited | Professional & scientific | 2013 |
| Selo Construction Ltd | Construction | 2024 |
| Selo Global Limited | Other services | 2023 |
| Selo Holdings Limited | Financial services | 2020 |
| Selvo Mart Ltd | Wholesale & retail | 2025 |
| Sema Jewellery Ltd | Wholesale & retail | 2024 |
| Semeraro Properties Limited | Real estate | 2025 |
| Semi Colon Inc Limited | Information & communication | 2015 |
| Semigo Care Services Limited | Health & social care | 2020 |
| Semitac Limited | Information & communication | 2005 |
| SEN Catering Services Ltd | Hospitality | 2019 |
| Sena Health Limited | Health & social care | 2023 |
| Senado Group Ltd | Wholesale & retail | 2023 |
| Senapt Assets Limited | Administrative & support | 2023 |
| Senapt Limited | Information & communication | 2016 |
| Senceive Limited | Information & communication | 2005 |
| Senero Company Limited | Wholesale & retail | 2021 |
| Senna Developments MK Ltd | Construction | 2024 |
| Sensat Ltd | Information & communication | 2015 |
| Sense Technical Services Limited | Construction | 2020 |
| Sensei Pro Flow Services Ltd | Water & waste | 2026 |
| Sensei's 7 Limited | Professional & scientific | 2014 |
| Sensible Spaces Ltd | Construction | 2017 |
| Sensient Flavors Limited | Manufacturing | 1980 |
| Sensient Technologies Limited | Professional & scientific | 1981 |
| Sential Limited | Arts & recreation | 2020 |
| Sentient Corporate Solutions Limited | Extraterritorial | 2021 |
| Sentient Labs Ltd | Information & communication | 2025 |
| Sentinel Asset Management Limited | Professional & scientific | 2023 |
| Sentino Limited | Wholesale & retail | 2023 |
| Sentio Media Limited | Information & communication | 2013 |
| Sentosa Services Ltd | Professional & scientific | 2023 |
| Sentry Envision Limited | Other services | 1992 |
| SEO Stack Ltd | Information & communication | 2023 |
| Seowebfy Ltd | Information & communication | 2025 |
| Sepro Robotique Limited | Administrative & support | 1991 |
| Sepsols Limited | Financial services | 2020 |
| Sept Noir Ltd | Real estate | 2025 |
| September Consulting Limited | Administrative & support | 2023 |
| Sequent Clothing Ltd | Wholesale & retail | 2026 |
| Serbus CNI Limited | Construction | 2005 |
| Serbus Group Limited | Financial services | 2022 |
| Serbus Health Limited | Information & communication | 2001 |
| Serbus Secure Limited | Financial services | 2022 |
| Serena Jean Straker Ltd | Extraterritorial | 2025 |
| Serendipity 2 Limited | Professional & scientific | 2001 |