| Speculations Enterprises Limited | Administrative & support | 2001 |
| Speycourt Investments Limited | Real estate | 1998 |
| Spheretrax Limited | Information & communication | 2022 |
| Spirella Ltd | Information & communication | 2022 |
| Spirit Bomb Limited | Information & communication | 2026 |
| Spmu Studio Hitchin Ltd | Other services | 2024 |
| Spoog Limited | Professional & scientific | 2021 |
| Sportivephoto Limited | Professional & scientific | 2009 |
| Spotless Cambridge Limited | Households | 2013 |
| Square EGG Limited | Information & communication | 2014 |
| Square One Leisure Group Ltd | Education | 2020 |
| Squat Stool Limited | Wholesale & retail | 2018 |
| SR Money Transfer Limited | Financial services | 2009 |
| SRA Group of Properties Limited | Real estate | 2026 |
| SRC Marine Consulting Ltd | Professional & scientific | 2019 |
| SRK Group Limited | Arts & recreation | 2016 |
| ST Albans Property Management Limited | Financial services | 2021 |
| ST Albans Theatre Services Limited | Arts & recreation | 2024 |
| ST Andrews (Hitchin) Management Company Limited | Households | 2014 |
| ST Germain's Barn Ltd | Arts & recreation | 2024 |
| ST James's House Residents Management Limited | Extraterritorial | 2015 |
| ST Lukes Development Limited | Real estate | 2022 |
| ST Mary's Church of England Academy, Stotfold | Education | 2012 |
| ST Paul's Walden PRE - School Limited | Education | 2004 |
| ST Pure Foods Ltd | Manufacturing | 2025 |
| ST. Elmo Flats Maintenance (Number 1) Limited | Households | 1984 |
| ST. Elmo Flats Maintenance (Number 2) Limited | Households | 1999 |
| ST. Michaels Road Hitchin (Blocks a, B, C, D, & E) Management Company Limited | Households | 1996 |
| ST. Swithin's Limited | Extraterritorial | 2003 |
| Stable Mind Yoga Ltd | Health & social care | 2021 |
| Stackallen Holdings Limited | Financial services | 2018 |
| Stackallen Investments Limited | Financial services | 2019 |
| Stackallen Limited | Administrative & support | 2018 |
| Stackallen Properties Limited | Construction | 2010 |
| Stag Construction & Roofing Ltd | Construction | 2026 |
| Stag Construction Group Ltd | Construction | 2024 |
| Stageswift Limited | Manufacturing | 2021 |
| Stagg Plumbing and Heating Limited | Extraterritorial | 2013 |
| Stagg Ridge Management Limited | Real estate | 2006 |
| Stancil Counselling and CBT Ltd | Health & social care | 2026 |
| Standards International Limited | Financial services | 2007 |
| Stanford Electrical Contractors Ltd | Construction | 2021 |
| Stark Property Management Ltd | Households | 2019 |
| Starlight Paediatrics Limited | Health & social care | 2001 |
| Starlings Bridge Properties Limited | Construction | 2002 |
| Startwell Engineering (U.K.) Limited | Manufacturing | 1992 |
| Statcore Ltd | Administrative & support | 2008 |
| STC Decorators Ltd | Construction | 2023 |
| Steelerule Limited | Information & communication | 1998 |
| Stem Together Limited | Information & communication | 2015 |
| Stemlux Limited | Professional & scientific | 2024 |
| Step UP to Beauty Limited | Other services | 2022 |
| Stepbel Ltd | Real estate | 2017 |
| Stephanie Prior School of Dancing Ltd | Education | 2010 |
| Steponeprocess Ltd | Public administration | 2024 |
| Steve Jump Ltd | Information & communication | 2016 |
| Steve Wooldridge Limited | Wholesale & retail | 2016 |
| Stevenage Cricket and Hockey Sports Club Ltd | Arts & recreation | 2025 |
| Stevenage Motor Centre Limited | Wholesale & retail | 2013 |
| Stevenage Roof Repairs & Roofers Ltd | Construction | 2023 |
| Stevenage Scrap Metal Limited | Wholesale & retail | 2014 |
| Stick and Rudder Ltd | Professional & scientific | 2017 |
| Stickland Associates Limited | Information & communication | 2023 |
| Stocks Carpentry Ltd | Construction | 2025 |
| Stolengrapefruit Limited | Professional & scientific | 2017 |
| Stomor EOT Limited | Financial services | 2025 |
| Stomor Ltd | Professional & scientific | 2007 |
| Stondon Classics Ltd | Real estate | 2015 |
| Stondon Ltd | Financial services | 2024 |
| Stoneheart Build Ltd | Construction | 2025 |
| Stoneroad Properties Limited | Real estate | 1996 |
| Stony INS Ltd | Hospitality | 2015 |
| Stopsley Property Management Limited | Households | 2018 |
| Stories Matter Limited | Other services | 2025 |
| Storm Counselling and Psychotherapy Ltd | Professional & scientific | 2021 |
| Stortford Exteriors Ltd | Construction | 2023 |
| Stotfold (Gwnl) Management Company Limited | Households | 2006 |
| Stotfold News Limited | Information & communication | 2015 |
| Strachan Property Services Limited | Real estate | 2021 |
| Stradale Sport Ltd | Manufacturing | 2004 |
| Straightforward Media Digital Limited | Professional & scientific | 2019 |
| Strand Property Services Limited | Manufacturing | 1995 |
| Stranger Expeditions Ltd | Information & communication | 2023 |
| Strategic Sport Consultancy Ltd | Professional & scientific | 2020 |
| Strathmore AVE Ltd | Hospitality | 2026 |
| Strathmore Pre-School | Education | 2010 |
| Stratten Investments Limited | Real estate | 2021 |
| Stratton House (Biggleswade) Management Limited | Households | 2003 |
| Stratum Energy Ltd | Energy | 2026 |
| Strawberry Mountain Limited | Real estate | 2023 |
| Strawberry REX Limited | Professional & scientific | 2025 |
| Street Food Monthly Ltd | Hospitality | 2026 |
| Strings Associates Limited | Information & communication | 1996 |
| Strong Crawl Limited | Administrative & support | 2021 |
| Stroud Actuarial Ltd | Professional & scientific | 2025 |
| Strova Clinical Services Ltd. | Health & social care | 2016 |
| Structsol Limited | Professional & scientific | 2001 |
| Stuart Consultancy Limited | Professional & scientific | 2001 |
| Stuart Peck Music Ltd | Information & communication | 2007 |
| Stuck in the Truck Ltd | Arts & recreation | 2025 |