| ST Albans Country Properties Ltd | Real estate | 2020 |
| ST Albans Independent College Limited | Education | 2004 |
| ST Albans Operating Company Limited | Wholesale & retail | 2014 |
| ST Albans Property Services Limited | Real estate | 2003 |
| ST Albans Signal Box Preservation Trust | Arts & recreation | 2003 |
| ST Albans Skip Hire Limited | Professional & scientific | 2000 |
| ST Albans Specsavers Limited | Wholesale & retail | 1993 |
| ST Albans Visionplus Limited | Wholesale & retail | 1993 |
| ST Albans Waste Management Limited | Professional & scientific | 2000 |
| ST George Kiro Mina Limited | Construction | 2003 |
| ST Georges School (Harpenden) Lettings Limited | Arts & recreation | 2002 |
| ST Margaret's Enterprises Limited | Arts & recreation | 2005 |
| ST Ouen Limited | Wholesale & retail | 2007 |
| ST. Albans Hairdesigners Limited | Other services | 2000 |
| ST. Albans Chambers Ltd | Professional & scientific | 2000 |
| ST. Albans Townsend Bowls & Tennis Club Limited | Arts & recreation | 1923 |
| ST. Andrew's Mews Management Limited | Households | 1998 |
| ST. Margarets Mead Management Company Limited | Households | 1999 |
| ST. Monica's Management Company (South) Limited | Households | 1976 |
| Stage Shop Limited | Extraterritorial | 2003 |
| Stallion Healthcare Ltd | Health & social care | 2024 |
| Stamford Capital Holdings Ltd | Financial services | 2025 |
| Stan Limited | Construction | 2002 |
| Stanborough Mews Management Company Limited | Real estate | 2000 |
| Stansted News Limited | Information & communication | 1988 |
| Stanta Services Limited | Real estate | 1987 |
| Star Fine Limited | Real estate | 2003 |
| Star Investment Properties Limited | Construction | 1993 |
| Star Technical Services Ltd | Information & communication | 2003 |
| Starbridge Group (National) Limited | Professional & scientific | 2025 |
| Start Evolving Limited | Professional & scientific | 2006 |
| Stash Construction Limited | Construction | 2007 |
| Stefos Estates Limited | Construction | 1973 |
| Stephen Urban Limited | Professional & scientific | 2004 |
| Sterling Estate Agents Limited | Real estate | 2001 |
| Sterling Fire Solutions Ltd | Manufacturing | 2022 |
| Sterlitzia Ltd | Real estate | 2006 |
| Steve Bainbridge Photography Limited | Professional & scientific | 2007 |
| Steven King Limited | Information & communication | 2002 |
| Stevenage FA Limited | Hospitality | 2021 |
| Stevenage Hair Care Limited | Other services | 2003 |
| Stevenage Sheet Metal Co. Limited | Manufacturing | 1993 |
| Stewarts Accountants Ltd | Professional & scientific | 2000 |
| Stewartson & Associates Limited | Administrative & support | 1996 |
| Stilegate Stud Limited | Agriculture & fishing | 2004 |
| Stirling Resolve Ltd | Professional & scientific | 2026 |
| Stokes Properties Limited | Real estate | 1997 |
| Stokvis Tapes Limited | Manufacturing | 2019 |
| Stone Hairdressing Limited | Other services | 2003 |
| Stonebridge Fold Management Company Limited | Households | 2008 |
| Stonebridge Training Services Limited | | 1985 |
| Stormproof Limited | Construction | 1985 |
| Stortford Therapy Space LLP | | 2024 |
| Storyvord AI Labs Ltd | Information & communication | 2025 |
| Strange Design Limited | Professional & scientific | 2003 |
| Strategic Associates Ltd. | Professional & scientific | 2001 |
| Strategy Financial Limited | Financial services | 2000 |
| Streamlife Properties Ltd | Real estate | 2018 |
| Streamlife Solutions Ltd | Professional & scientific | 2018 |
| Streamroute Limited | Households | 1991 |
| Streetwise Self-Defence Limited | Education | 1998 |
| Strictly People Ltd | Administrative & support | 2006 |
| Strong Hair Emblem Ltd | Wholesale & retail | 2020 |
| Stronge Developments Ltd | Real estate | 2005 |
| Stuart Cross Maintenance Services Limited | Construction | 2007 |
| Student Journal Limited | Wholesale & retail | 2005 |
| Studio 12 London Ltd | Other services | 2008 |
| Studio Diba Salam Limited | Professional & scientific | 2009 |
| Studio N20 Ltd | Arts & recreation | 2025 |
| Studio Notion Ltd | Information & communication | 2024 |
| Stylin Productions Limited | Information & communication | 2002 |
| Subari Retail Ltd | Wholesale & retail | 2021 |
| SUE White Consultants Limited | Professional & scientific | 2001 |
| Suffolk Car Park Holdings Ltd | Transport & logistics | 2025 |
| Sunny Side Store Ltd | Wholesale & retail | 2023 |
| Sunnyday Blinds Limited | Wholesale & retail | 2005 |
| Sunray Estates Limited | Construction | 2004 |
| Sunrise UK Business Solutions Limited | Professional & scientific | 2017 |
| Superavi Ltd | Information & communication | 2014 |
| Supercurry Ltd | Hospitality | 2018 |
| Supply the Nation Limited | Wholesale & retail | 2015 |
| Supreme IT Services Limited | Professional & scientific | 2015 |
| Surgewispdecor Ltd | Wholesale & retail | 2025 |
| Surrey Car Park Holdings Ltd | Transport & logistics | 2025 |
| Susan Stewart & Co | | 1996 |
| Swanlea Limited | Real estate | 1990 |
| Swfs Limited | Financial services | 2007 |
| SY Music Ltd | Information & communication | 2007 |
| Sykes Engineering Services Limited | Professional & scientific | 2007 |
| Sylvester A.V. Services Ltd | Wholesale & retail | 2002 |
| Symban Limited | Real estate | 2001 |
| Symon Smith Ltd. | Real estate | 1998 |
| Synchro Solutions Ltd | Professional & scientific | 2000 |
| Syscity Limited | Information & communication | 1998 |
| T and C (Services) Limited | Real estate | 2000 |
| T Ward Properties Ltd | Real estate | 2018 |
| T. S. Mclaughlin & SON Limited | Construction | 2007 |
| T.S.K.A. (GB) Ltd | Arts & recreation | 1996 |
| Tailflareco Ltd | Wholesale & retail | 2025 |
| Tailwispcraft Ltd | Wholesale & retail | 2025 |