| S&T Catering Ltd | Hospitality | 2024 |
| S. Camp Investments Ltd | Real estate | 2024 |
| S. Camp Send Support Limited | Education | 2024 |
| S.E.E.M.S Flooring Ltd | Construction | 2017 |
| S.G.Wootton & Sons Limited | Agriculture & fishing | 1947 |
| S.P. Saban Ltd | Construction | 2001 |
| SA Credit Recovery Ltd | Administrative & support | 2019 |
| SAE Surveying Limited | Professional & scientific | 2018 |
| Safe & Secure 24/7 Limited | Administrative & support | 2017 |
| Safe Cracker Ltd | Manufacturing | 2014 |
| Safegas London Limited | Construction | 2016 |
| Saffren Interiors Limited | Construction | 2004 |
| Saffronlily Limited | Real estate | 2018 |
| Sail Away Media Ltd | Information & communication | 2023 |
| Salacia Limited | Construction | 2000 |
| Salacia South East Limited | Real estate | 2017 |
| Sales Recruitment Solutions Ltd | Administrative & support | 2018 |
| Salt Property Maintenance Ltd | Construction | 2025 |
| Saltie Studios Ltd | Arts & recreation | 2023 |
| Salvcivils Ltd | Construction | 2026 |
| Salyx Care Limited | Health & social care | 2020 |
| Sanctuary Lettings & Management Ltd | Real estate | 2017 |
| Sand Capital Limited | Real estate | 2019 |
| Sands Financial Management Limited | Financial services | 2014 |
| SAP Book-Keeping Ltd | Professional & scientific | 2021 |
| Sapphire Developments Solihull Ltd | Real estate | 2017 |
| Sarah Riley Properties Ltd | Real estate | 2025 |
| Sarah Waddington Solicitors Ltd | Professional & scientific | 2014 |
| Sariyer Properties Limited | Real estate | 2006 |
| Savrim Legal Consultancy Limited | Professional & scientific | 2019 |
| SBS OIL and GAS Limited | Construction | 2013 |
| Scenic Brothers Ltd | Construction | 2020 |
| SCF Solutions Limited | Professional & scientific | 2019 |
| Schertel AVL Ltd | Professional & scientific | 2025 |
| Schertel Build Ltd | Construction | 2024 |
| School of Sensual Arts Limited | Other services | 2023 |
| Scootours Limited | Administrative & support | 2020 |
| Scran and Barrel Ltd | Hospitality | 2024 |
| Scroll & Stop Limited | Wholesale & retail | 2024 |
| Scrumptious Cafe Ltd | Hospitality | 2025 |
| Sculpted & Skin Ltd | Health & social care | 2025 |
| Sealey Productions Ltd | Information & communication | 2015 |
| Sean Stone Holdings Ltd | Financial services | 2024 |
| Second Round Ltd | Administrative & support | 2021 |
| Second SET Solutions Ltd | Hospitality | 2024 |
| Secure-Ops Events Ltd | Administrative & support | 2020 |
| Seen Holdings Ltd | Financial services | 2023 |
| Seen Renewables Ltd | Construction | 2023 |
| Select Systems London Limited | Administrative & support | 2019 |
| Sensory Solutions Herbal Evolution C.I.C. | Education | 2018 |
| Seona Thomson Coaching Ltd | Professional & scientific | 2023 |
| Serendipity Hertford Ltd | Hospitality | 2019 |
| Seroge Limited | Extraterritorial | 2010 |
| Sett and Warren Ltd | Transport & logistics | 2022 |
| Settdown Aviation Ltd | Manufacturing | 2025 |
| Seven Nine Design Services Ltd | Professional & scientific | 2017 |
| Sfizio Restaurants Limited | Hospitality | 2002 |
| SG Collective Ltd | Real estate | 2025 |
| SG11 Productions Limited | Arts & recreation | 2025 |
| SH GPH Ltd | Construction | 2025 |
| Shadow Adventures Ltd | Arts & recreation | 2026 |
| Sharks Rugby Limited | Other services | 2013 |
| Sheepcote Management Limited | Extraterritorial | 2006 |
| Sheer Content Creation Limited | Professional & scientific | 2022 |
| Shelton Building and Maintenance Limited | Construction | 2015 |
| Shenleys Management Company Limited | Households | 2019 |
| Shield Accountancy Services Limited | Professional & scientific | 2014 |
| Shield CIS Limited | Construction | 2024 |
| Shield Contract Services (UK) Limited | Construction | 2010 |
| Shield Contract Services Limited | Construction | 2011 |
| Shield Group Holdings Limited | Professional & scientific | 2015 |
| Shield Group Investments Limited | Professional & scientific | 2014 |
| Shinnovation Limited | Professional & scientific | 2014 |
| Shorecart Ltd | Wholesale & retail | 2026 |
| Shove Turnparts Limited | Manufacturing | 1948 |
| SHR Decorating Ltd | Construction | 2024 |
| Shuttle Media Ltd | Information & communication | 2017 |
| Sikaman Limited | Health & social care | 2014 |
| Silver Leys Arena Polo Limited | Real estate | 2016 |
| Silver Leys Events Limited | Other services | 2012 |
| Simavin Limited | Wholesale & retail | 2013 |
| SIMO82 Business Ltd | Transport & logistics | 2025 |
| Simpliprocurement Ltd | Wholesale & retail | 2025 |
| Simpliservices Limited | Manufacturing | 2024 |
| Simply Carpets Limited | Wholesale & retail | 1991 |
| Simprop Limited | Hospitality | 2020 |
| Sisters Designs (LDN) Ltd | Wholesale & retail | 2026 |
| SJI Connect Ltd | Transport & logistics | 2017 |
| SK Executive Car Service Ltd | Transport & logistics | 2023 |
| Skidmores Aftercare Limited | Administrative & support | 2013 |
| Skidmores of Hertford Limited | Construction | 1992 |
| Skillmed Recruitment and Outsourcing Ltd | Administrative & support | 2022 |
| Skintec Holdings Ltd | Financial services | 2025 |
| Sky Roofing (Hertford) Ltd | Construction | 2012 |
| Slovar Limited | Professional & scientific | 2003 |
| Smart Business Group Ltd | Administrative & support | 2019 |
| Smart Premier Cleaning Services Limited | Administrative & support | 2022 |
| Smarter Homes (Anglia) Ltd | Wholesale & retail | 2012 |
| Smiling Bright Ltd | Health & social care | 2020 |
| Smith Fieldsports Ltd | Administrative & support | 2021 |