| S&S Autotech Ltd | Wholesale & retail | 2025 |
| S. & R. (London) Ltd. | Construction | 1990 |
| S.W. Plastics Limited | Manufacturing | 1986 |
| S10 Companies Ltd | Financial services | 2024 |
| Saebo UK Limited | Health & social care | 2005 |
| Safe CAB Airport Taxi Ltd | Transport & logistics | 2024 |
| Safe in Construction Ltd | Construction | 2025 |
| Safe Space Movement | Health & social care | 2021 |
| Safet-Net | Education | 2009 |
| Saffron Park (Thaxted Road) Management Company Limited | Households | 2025 |
| Sales Economics Limited | Information & communication | 2025 |
| Sallet Consulting Limited | Professional & scientific | 2001 |
| Salvation House Limited | Hospitality | 2013 |
| Sameth Properties Limited | Professional & scientific | 2005 |
| Samson Rigging Services Limited | Construction | 2015 |
| Sanity Trustees Limited | Professional & scientific | 2006 |
| Sara Haddock Ltd | Professional & scientific | 2024 |
| Sarah James Plastering and Damp Proofing Ltd | Construction | 2026 |
| Saratota Limited | Administrative & support | 2005 |
| Sari Group Ltd | Real estate | 2021 |
| Sarnafil Roof Assured Limited | Wholesale & retail | 1993 |
| Sarvajeyam Solutions Limited | Information & communication | 2009 |
| SAS Plumbing Heating & Electrical Ltd | Construction | 2019 |
| Sathuta-Mage | Health & social care | 2022 |
| Satsang CIC | Other services | 2024 |
| Saunders Partnership Design Limited | Professional & scientific | 2005 |
| Saunders Partnership Limited | Professional & scientific | 1989 |
| Sava London Limited | Professional & scientific | 2021 |
| SBX Systems Consulting Limited | Professional & scientific | 2024 |
| Scarab Jewels Ltd | Information & communication | 2018 |
| Scenic Railways Limited | Arts & recreation | 2001 |
| Scent Nation Ltd | Wholesale & retail | 2022 |
| Scholars Management Company Limited | Households | 2020 |
| School Consulting Ltd | Education | 2018 |
| Scorpio Logistics Limited | Wholesale & retail | 2021 |
| Scott Willmott Consultancy Ltd | Real estate | 2021 |
| Scribbles Nursery Limited | Education | 2003 |
| Scrubzbyzs Ltd | Wholesale & retail | 2018 |
| Scully Roofing Ltd | Construction | 2018 |
| Seacroft Green Nominee 1 Ltd | Administrative & support | 2001 |
| Seacroft Green Nominee 2 Ltd | Administrative & support | 2001 |
| Seamless Connectiv Consulting Ltd | Information & communication | 2025 |
| Sean Reed Painters & Decorators Ltd | Construction | 2011 |
| Second Sight Associates Limited | Manufacturing | 2014 |
| Secret Garden Quilting Ltd | Wholesale & retail | 2011 |
| Securi-Doors Services Limited | Construction | 2004 |
| Seers Limited | Professional & scientific | 1996 |
| Seldur Ltd | Real estate | 2025 |
| Selene and Partners Limited | Wholesale & retail | 2023 |
| Seller Magnify Ltd | Wholesale & retail | 2024 |
| Semanaj Brothers Property Limited | Real estate | 2025 |
| Semeris Limited | Information & communication | 2020 |
| Sendly CIC | Information & communication | 2024 |
| Senter Limited | Information & communication | 2016 |
| Sentrilink Security Ltd | Construction | 2026 |
| Serendib Ltd | Real estate | 2022 |
| Serenity Lifestyle Ltd | Wholesale & retail | 2026 |
| Seven Design Ltd | Administrative & support | 2010 |
| Seven Peaks Analytics Limited | Information & communication | 2025 |
| Seymour Service Solutions Ltd | Information & communication | 2013 |
| SF Roofing Ltd | Construction | 2009 |
| SFP Property and Estate Management Ltd | Real estate | 2009 |
| SG Consulting Partners Ltd | Professional & scientific | 2026 |
| SHA Cleaning Services Ltd | Administrative & support | 2023 |
| Shadow Lock Ltd | Wholesale & retail | 2026 |
| Shadz Care Ltd | Health & social care | 2018 |
| Shakchow Limited | Information & communication | 2021 |
| Shale T14 Ltd | Other services | 2020 |
| Shanx Ltd | Arts & recreation | 2026 |
| Sharana & Co PVT Ltd | Real estate | 2024 |
| Sharp Search Ltd | Professional & scientific | 2023 |
| Shaun Collins Golf Ltd | Arts & recreation | 2021 |
| Shelford Technologies Ltd | Information & communication | 2025 |
| Shenny Technologies Limited | Information & communication | 2014 |
| Sheridans Howardsgate Ltd | Professional & scientific | 2020 |
| Sherrards Management (Mansion) Limited | Administrative & support | 1995 |
| Sherrards Management (Mews) Limited | Households | 1995 |
| Sherrardswood Park Management Company Limited | Administrative & support | 1997 |
| SHIFT2ZERO Ltd | Information & communication | 2022 |
| Shine-V Ltd | Wholesale & retail | 2015 |
| Shipxi International Limited | Transport & logistics | 2025 |
| Shire & City Ltd | Administrative & support | 2014 |
| Shire Heating Limited | Construction | 2023 |
| Shivam Consultancy Ltd | Information & communication | 2021 |
| Shree Siddhivinayak Limited | Wholesale & retail | 2020 |
| Shristi IT Ltd | Information & communication | 2019 |
| Siciliano Barbers Limited | Other services | 2015 |
| Sidel (UK) Limited | Manufacturing | 2001 |
| Sigma Imaging (UK) Limited | Manufacturing | 2000 |
| Signature Collectables Ltd | Wholesale & retail | 2023 |
| Signeto Limited | Construction | 2010 |
| Signia Care Homes Limited | Professional & scientific | 2003 |
| Signia Developments Limited | Construction | 2004 |
| Silicon Connect Ltd | Wholesale & retail | 2009 |
| Silk&Dew Ltd | Other services | 2021 |
| Silver Coast Consulting Limited | Information & communication | 2021 |
| Silver FOX Group Ltd | Financial services | 2020 |
| Silver FOX Labeling Limited | Manufacturing | 2023 |
| Silver FOX Limited | Manufacturing | 1977 |
| Silver Lion Europe Ltd | Wholesale & retail | 2014 |