| SCS Scaffolding (Anglia) Limited | Construction | 2012 |
| Scully Homes Ltd | Real estate | 2020 |
| Scumbag Tactical Ltd | Wholesale & retail | 2025 |
| Scupa Ltd | Hospitality | 2023 |
| Scyldan Ltd | Financial services | 2025 |
| SD Barber Interiors Limited | Construction | 2013 |
| SD Electrical Solutions Ltd | Construction | 2022 |
| SD Property Ventures Ltd | Real estate | 2021 |
| SD Ssas Ltd | Agriculture & fishing | 2011 |
| SDB Enterprises Essex Ltd | Manufacturing | 2026 |
| Sdcookelectrical Ltd | Construction | 2023 |
| SDF Mechanical Services Ltd | Construction | 2020 |
| SDH 3RD GEN Ltd | Transport & logistics | 2021 |
| SDS Events Ltd | Education | 2025 |
| SDS Smart Surveys Limited | Professional & scientific | 2022 |
| SDS Surrey Ltd | Information & communication | 2014 |
| SDT Construction Ltd | Construction | 2026 |
| SE Cantonese Limited | Hospitality | 2023 |
| SE Colchester Property Ltd | Financial services | 2025 |
| SE Healthcare Provider Limited | Health & social care | 2021 |
| SE Long Consulting Ltd | Administrative & support | 2021 |
| Seacare Investments Limited | Real estate | 2023 |
| Seaford Properties Limited | Construction | 1984 |
| Seager Investments Limited | Real estate | 2018 |
| Seago Kitchens Ltd | Construction | 2016 |
| Seagoat Property Services Ltd | Hospitality | 2025 |
| Seagrove Management Company Limited | Households | 2014 |
| Sealey (UK) Limited | Financial services | 1990 |
| Sean Davies Motorcycles Service and Repairs Ltd | Manufacturing | 2011 |
| Sean E Brown Ltd | Health & social care | 2021 |
| Sean Ferriter Medical Ltd | Health & social care | 2018 |
| Seapol Limited | Wholesale & retail | 2019 |
| Seascape Brightlingsea Ltd | Hospitality | 2015 |
| Seaview 42 Ltd | Real estate | 2015 |
| Seaview House Care Ltd | Health & social care | 2008 |
| Seaview House Clacton Ltd | Real estate | 2019 |
| Seawise Chartering Limited | Transport & logistics | 1985 |
| Seax Security Ltd | Administrative & support | 2018 |
| Sebclean Limited | Administrative & support | 2026 |
| Seby Trans Ltd | Construction | 2019 |
| SEC & Soft Solutions Ltd | Information & communication | 2025 |
| Seckford Agencies Limited | Wholesale & retail | 1996 |
| Second Beach Consulting Limited | Professional & scientific | 2016 |
| Second Bridge Property Ltd | Real estate | 2016 |
| Second Phase Digital Ltd | Information & communication | 2019 |
| Seconds OUT Songs Ltd | Information & communication | 2026 |
| Secret Bunker Management Company Limited | Households | 2020 |
| Secretarial Solutions (Langham) Limited | Administrative & support | 2003 |
| Secure Retirement Limited | Financial services | 2024 |
| Secure Server Solutions Limited | Information & communication | 2020 |
| Secure Shipments Ltd | Transport & logistics | 2023 |
| Securesoft Limited | Other services | 2019 |
| Sedoy Ltd | Construction | 2026 |
| SEE the Show Merch Limited | Administrative & support | 2026 |
| Seeba Consultancy Limited | Health & social care | 2025 |
| Seeds of Ayllu Limited | Extraterritorial | 2019 |
| Sees Holdings Ltd | Financial services | 2018 |
| Sefil Housing Ltd | Real estate | 2024 |
| Seismic Construction Ltd | Construction | 2026 |
| Seivad (Holdings) Limited | Professional & scientific | 1964 |
| Sekura Global Holdings Ltd | Wholesale & retail | 2020 |
| Sekura Global IP LLP | | 2011 |
| Sekura Global Limited | Wholesale & retail | 2018 |
| Sekura Management Limited | Wholesale & retail | 2020 |
| Selawik Retail Ltd | Administrative & support | 2016 |
| Select Properties (Colchester) Limited | Administrative & support | 2008 |
| Select Safety Services (UK) Limited | Professional & scientific | 2017 |
| Selectacars Limited | Wholesale & retail | 2002 |
| Selin Transport Ltd | Transport & logistics | 2023 |
| Selkirk Retail Ltd | Wholesale & retail | 2026 |
| Sellby Homes Limited | Real estate | 2024 |
| Sellen Consulting Ltd | Professional & scientific | 2017 |
| Semarc International Limited | Professional & scientific | 1994 |
| Send Support East Ltd | Education | 2025 |
| Send Supportive Pathways Ltd | Health & social care | 2026 |
| Sendsimply Holdings Limited | Wholesale & retail | 2020 |
| Senergy Bounce Ltd | Arts & recreation | 2025 |
| Sengda Freight Ltd | Transport & logistics | 2023 |
| Sensational Learning Ltd | Education | 2025 |
| Sensational Minds Ltd | Professional & scientific | 2019 |
| Sensetrade Limited | Other services | 1984 |
| Sensory Beginnings Tendring Ltd | Education | 2024 |
| Sensorybeginningscolchester Ltd | Education | 2024 |
| SEP Developments Ltd | Construction | 2025 |
| Septagram Games Ltd | Information & communication | 2023 |
| Sequoia Capital Ltd | Real estate | 2025 |
| Serene Health and Wellness Ltd | Health & social care | 2020 |
| Serenity Book Publishing Limited | Information & communication | 2024 |
| Serenity Brides Outlet Limited | Other services | 2019 |
| Serenix Consulting Ltd | Health & social care | 2025 |
| Serenum Services Limited | Wholesale & retail | 2021 |
| Serge Denimes Ltd | Administrative & support | 2010 |
| Serif Design and Communications Limited | Information & communication | 2007 |
| Serious-Rc Limited | Wholesale & retail | 2021 |
| Service Integrity & Logistics Limited | Health & social care | 2022 |
| Serviced Homes London Ltd | Real estate | 2024 |
| SES Mechanical Group Limited | Professional & scientific | 2023 |
| SES Mechanical Holdings Ltd | Financial services | 2021 |
| SES Mechanical Limited | Professional & scientific | 2000 |
| SES Mechanical Services Holdings Ltd | Financial services | 2021 |