| Sirin Hertford Ltd | Hospitality | 2025 |
| SIX Morgans Limited | Real estate | 2020 |
| Siân & Adam the Home Improvers Ltd | Construction | 2018 |
| SJ Electrical Contractors Limited | Construction | 2019 |
| Sjjh Investors Limited | Financial services | 2025 |
| SJK & Partners Limited | Administrative & support | 2022 |
| SJL Heating Limited | Construction | 2012 |
| SJN Consulting Ltd | Professional & scientific | 2020 |
| SJP SAP Consulting Limited | Information & communication | 2011 |
| Skillbrokers Prima Resourcing Limited | Administrative & support | 2001 |
| Skillgroup Limited | Construction | 1987 |
| Skills N Consult Ltd | Professional & scientific | 2023 |
| Skills Ready Hub Ltd | Administrative & support | 2025 |
| Skin & Bare Ltd | Other services | 2024 |
| SKN LAB Aesthetics Ltd | Education | 2019 |
| SKP Consultancy Ltd | Professional & scientific | 2024 |
| Skpts Partnership Limited | Administrative & support | 2015 |
| Skyreach Limited | Professional & scientific | 2004 |
| Skyscraper Music Limited | Information & communication | 2024 |
| Skyshoot Ltd | Professional & scientific | 2021 |
| Skyview Roofing & Aerial Imaging Solutions Limited | Construction | 2025 |
| Slater Bros. Plumbing & Heating Ltd | Construction | 2017 |
| Sleipnir Consulting Limited | Administrative & support | 2015 |
| Slice City Ltd | Hospitality | 2025 |
| Smart Auto Solutions Ltd | Administrative & support | 2015 |
| Smart Installation Services Ltd | Administrative & support | 2017 |
| Smart Lenders Asset Management Limited | Administrative & support | 2011 |
| Smart Merchants Ltd | Wholesale & retail | 2010 |
| Smartcare Services Limited | Health & social care | 2004 |
| Smartline Kitchens Ltd | Construction | 2019 |
| Smartlite Limited | Administrative & support | 2014 |
| Smith's Construction (London) Ltd | Professional & scientific | 2018 |
| SMJ Finance Director Services Ltd | Professional & scientific | 2012 |
| Snapful Ltd | Wholesale & retail | 2024 |
| SNE Management Limited | Arts & recreation | 2006 |
| Snout Music Limited | Arts & recreation | 1995 |
| SO Naturally Ltd | Administrative & support | 2010 |
| Social Mediadent Ltd | Professional & scientific | 2020 |
| Social Solar Power Limited | Professional & scientific | 2010 |
| Society of Motion Pictures and Television Engineers; Smpte Limited | Other services | 2013 |
| Socrates Systems Ltd | Information & communication | 2008 |
| Sofa Club Limited | Wholesale & retail | 2012 |
| Software Services (UK) Limited | Information & communication | 2004 |
| Soho Dispensers Limited | Wholesale & retail | 2009 |
| Soibev Limited | Administrative & support | 2025 |
| Solace Holdings Ltd. | Administrative & support | 2017 |
| Somersham Self Storage Limited | Administrative & support | 2025 |
| Sonas Recruitment & Management Services Ltd | Professional & scientific | 2024 |
| Sonoscope Limited | Health & social care | 2016 |
| Sorted Ventures International Limited | Information & communication | 2014 |
| Sorted Ventures Ltd | Information & communication | 2007 |
| SOS Car Finder Limited | Wholesale & retail | 2019 |
| Sound Live Limited | Administrative & support | 2025 |
| Source and Drive Limited | Wholesale & retail | 2025 |
| Source Your Sherpa Ltd | Administrative & support | 2025 |
| Souters International Ltd | Real estate | 2006 |
| South Herts Plumbing & Heating Limited | Construction | 2010 |
| Southern Cross Flooring Limited | Construction | 2018 |
| Southgate Production Ltd | Arts & recreation | 2023 |
| Sovereign Place Estate Management Company (Limehouse) Limited | Households | 1998 |
| Sowerby Hall Consulting Limited | Professional & scientific | 2015 |
| Space for Learning Ltd | Professional & scientific | 2015 |
| Spanico Enterprises Limited | Professional & scientific | 2006 |
| Sparkle Cleaning Solutions Limited | Administrative & support | 2017 |
| Sparkpine Limited | Wholesale & retail | 2022 |
| Sparrow and Vale Farm Entrance Ltd | Real estate | 2025 |
| Specialist in Events Limited | Professional & scientific | 2026 |
| Spectrum of Misconception CIC | Administrative & support | 2020 |
| Speedflow Plumbing Services Ltd | Construction | 2019 |
| SPG Supplies Limited | Administrative & support | 2012 |
| Spice HUT (Hertford) Ltd | Hospitality | 2019 |
| Spirited Management Ltd | Wholesale & retail | 2023 |
| Spooner Bioanalytical Solutions Ltd | Professional & scientific | 2015 |
| Sporting Events Solutions Limited | Administrative & support | 2012 |
| Sports & Leisure Boxing Limited | Extraterritorial | 2002 |
| Sports and Spinal Physio Limited | Health & social care | 2010 |
| Sports Prototype Racecars Limited | Manufacturing | 2018 |
| Spotlight Art Limited | Wholesale & retail | 2022 |
| Spotlight Technology Ltd | Professional & scientific | 2004 |
| Spotlight Weddings Limited | Information & communication | 2012 |
| Spring Medical Writing Ltd | Professional & scientific | 2020 |
| Springfield Park Management Company Limited | Real estate | 2018 |
| Springlock Ltd | Manufacturing | 1996 |
| Spud Commercial Limited | Real estate | 2013 |
| Squires Ridge Management Co. Limited | Real estate | 1986 |
| SRF Property Management Limited | Real estate | 2018 |
| SRM Connect Ltd | Construction | 2018 |
| SRS Engineering Limited | Manufacturing | 2011 |
| SSA Analysis Limited | Administrative & support | 2016 |
| SSB Aesthetics Limited | Health & social care | 2023 |
| Ssgre Solutions Ltd | Administrative & support | 2017 |
| SSL Solutions Ltd | Administrative & support | 2024 |
| ST Cross Chambers Management Limited | Real estate | 1996 |
| ST Cross Developments Limited | Real estate | 1996 |
| ST Cross Estates (Holdings) Limited | Financial services | 2006 |
| ST David's Court Management (Middlesex) Limited | Households | 2004 |
| ST John's ROW Number 1 Management Company Limited | Households | 2006 |
| ST Pauls Court RTM Company Limited | Households | 2008 |
| ST. John's Westminster RTM Company Limited | Households | 2003 |
| ST. Michaels Road Hitchin (Blocks F & G) Management Company Limited | Households | 1996 |