| Seal Estates Limited | Real estate | 1933 |
| Seal Logistics Limited | Transport & logistics | 2026 |
| Seal Midco 1 Limited | Financial services | 2017 |
| Seal Midco 2 Limited | Financial services | 2017 |
| Seal Topco Limited | Financial services | 2017 |
| Seale Medical Ltd | Health & social care | 2025 |
| Seamariner Limited | Administrative & support | 1992 |
| Seamariner (WB) Limited | Administrative & support | 2020 |
| Seamark Marine Ltd | Transport & logistics | 2026 |
| Seamless DMP Limited | Wholesale & retail | 2018 |
| Seamless Projects Ltd | Construction | 2022 |
| Sean DU Plessis Limited | Professional & scientific | 2023 |
| Sean Grimshaw Ltd | Transport & logistics | 2013 |
| Search Breeze Ltd | Wholesale & retail | 2021 |
| Search Media Ltd | Information & communication | 2024 |
| Searoni Limited | Professional & scientific | 2025 |
| Seasonal Solutions Ltd | Wholesale & retail | 2023 |
| Seasouth Builds Limited | Transport & logistics | 2025 |
| Seastreet Ltd | Hospitality | 2019 |
| Seatech Commercial Diving Services Limited | Administrative & support | 2000 |
| Seatech Holdings Limited | Administrative & support | 2008 |
| Seatech Rentals Ltd | Real estate | 2024 |
| Seatech Solutions Ltd | Professional & scientific | 2014 |
| Seavacations Limited | Administrative & support | 1998 |
| Seavacations UK Limited | Administrative & support | 1998 |
| Seaview Arboriculture Ltd | Agriculture & fishing | 2022 |
| Seaway Group Limited | Professional & scientific | 2001 |
| Seaweed Close Limited | Real estate | 2004 |
| Seb&Flo Trans Ltd | Transport & logistics | 2025 |
| Seba Transport (Reading) Limited | Transport & logistics | 2019 |
| Sebastian Distribution Ltd | Wholesale & retail | 2020 |
| Sebco P&D Ltd | Other services | 2014 |
| Sebexpress Ltd | Transport & logistics | 2014 |
| Sebo Ltd | Construction | 2015 |
| Seby DEP MET Ltd | Transport & logistics | 2021 |
| SEC Consulting Limited | Information & communication | 2004 |
| Second Avenue Business Park Limited | Real estate | 1994 |
| Secure Design Windows Doors Ltd | Construction | 2023 |
| Secure Telecommunications Ltd | Information & communication | 2020 |
| Secured Intelligence Ltd | Wholesale & retail | 2017 |
| Securefire Solutions Ltd | Administrative & support | 2015 |
| Security Disposal Limited | Administrative & support | 2000 |
| Security Elements Limited | Administrative & support | 2020 |
| Security Nation Ltd | Administrative & support | 2011 |
| Security Onsite Ltd | Administrative & support | 2019 |
| Security Self Storage Limited | Transport & logistics | 2002 |
| Security Southampton Limited | Construction | 2021 |
| Sedgemead Property Management Limited | Administrative & support | 1984 |
| Sedna Property Investments Limited | Construction | 2003 |
| Seedfund Limited | Professional & scientific | 2006 |
| Seemas Beauty Salon Ltd | Other services | 2023 |
| Seer HOR Ltd | Health & social care | 2014 |
| Seevent Plastics Holdings Limited | Manufacturing | 2014 |
| SEG Services Ltd | Construction | 2024 |
| Segensworth Court, Fareham Management Company Limited | Households | 2016 |
| Segensworth Motor Company Ltd | Wholesale & retail | 2020 |
| Seghir Limited | Transport & logistics | 2017 |
| Segrave Holdings 2 Ltd | Construction | 2017 |
| Segrave Management Services Limited | Real estate | 2022 |
| Segrave Saxley 2 Ltd | Real estate | 2022 |
| Segrave Saxley Management Ltd | Administrative & support | 2018 |
| Seguro Technology Limited | Information & communication | 2024 |
| Seivad Foods Limited | Administrative & support | 2017 |
| Selborne Court (Romsey) Limited | Households | 1976 |
| Select Bakers Ltd | Wholesale & retail | 2024 |
| Select CAD Services Ltd | Information & communication | 2011 |
| Select Cars Ltd | Wholesale & retail | 2010 |
| Selectatee Ltd | Manufacturing | 2023 |
| Selected Ltd | Other services | 2016 |
| Selene Creative Adverts Limited | Manufacturing | 2026 |
| Self Marine Technology Ltd | Manufacturing | 2022 |
| Selfie Wizard Limited | Professional & scientific | 2017 |
| Selimi Ltd | Wholesale & retail | 2025 |
| Sell & Repair IT Limited | Other services | 2022 |
| Sell Stuff Today Limited | Wholesale & retail | 2012 |
| Selling Sun Ltd | Information & communication | 2021 |
| Selly's Southampton Limited | Other services | 2018 |
| Selmora Ltd | Health & social care | 2026 |
| Selvamall Ltd. | Wholesale & retail | 2017 |
| Selvanayakam Ltd | Wholesale & retail | 2025 |
| SEM Enterprises Limited | Professional & scientific | 2014 |
| Semantic Limited | Information & communication | 1999 |
| Semantic SEO Digital Ltd | Information & communication | 2025 |
| Semas Solutions Ltd | Construction | 2024 |
| Semboleletrical Ltd | Construction | 2026 |
| Semco Teak Products (UK) Limited | Wholesale & retail | 2002 |
| Semco-Holdings Limited | Financial services | 2025 |
| SEME4 Limited | Information & communication | 2004 |
| Semi Permanent Make UP @ Studio 7 Limited | Other services | 2015 |
| Semico Technologies Ltd | Manufacturing | 2024 |
| Semigon Consultancy Limited | Wholesale & retail | 2025 |
| Semnoo Ltd | Administrative & support | 2024 |
| Semp Locums Private Ltd | Health & social care | 2015 |
| Semsu C.I.C. | Arts & recreation | 2025 |
| SEN Consultancy Limited | Construction | 2020 |
| SEN Property Ltd | Construction | 2025 |
| Senator Security Limited | Administrative & support | 2025 |
| Send Telecoms Group Ltd | Information & communication | 2025 |
| Sendit Group Ltd | Wholesale & retail | 2018 |
| Sendsational Ltd | Education | 2022 |