| Speedwell Associates Limited | Information & communication | 1994 |
| Speedwell Settlement Services Limited | Financial services | 2016 |
| Spencer Presentations Limited | Arts & recreation | 1997 |
| SPN Consultancy Limited | Information & communication | 2004 |
| Sporting Hands Massage Limited | Health & social care | 2016 |
| Sports Capital Operations Limited | Information & communication | 2025 |
| Sports Park Creations Ltd | Professional & scientific | 2025 |
| Sporty Origins Ltd | Manufacturing | 2025 |
| Spot Global Investment Limited | Professional & scientific | 2010 |
| Spothaven Property Management Limited | Households | 2000 |
| Spotlight on Africa Investments Limited | Professional & scientific | 2026 |
| Springview Ranges Limited | Wholesale & retail | 2013 |
| Spritzers Limited | Arts & recreation | 1989 |
| SPS Cambodian Foundation Limited | Hospitality | 2010 |
| Sqlbits Limited | Information & communication | 2007 |
| Square Feet Holdings Ltd | Construction | 2024 |
| SRC Estates Management Ltd | Real estate | 2021 |
| SRC Property Development Ltd | Real estate | 2019 |
| ST Albans Stockbrokers Ltd | Financial services | 2013 |
| ST Financial Limited | Professional & scientific | 2015 |
| ST George's School, Harpenden Academy Trust | Education | 2012 |
| ST Georges Residential Lettings Limited | Hospitality | 2009 |
| ST Georges School (Harpenden) Limited | Education | 1945 |
| ST Helena's Court Management Company Limited | Households | 2006 |
| ST Michaels 8 Ltd | Professional & scientific | 2021 |
| ST Peter's Square Management Limited | Households | 1999 |
| ST. Leonards Management Company Limited | Households | 1991 |
| St.Albans Taxis Ltd | Transport & logistics | 2018 |
| St.Nicholas Court Residents' Association Limited | Households | 1970 |
| Stable Mews Management Limited | Households | 1992 |
| Staceys Accountants Limited | Professional & scientific | 2017 |
| STAGE-2 Consulting Limited | Professional & scientific | 2016 |
| Stahl FE Ltd | Professional & scientific | 2023 |
| Stakers Court Limited | Households | 2023 |
| Stand UP Consulting Ltd | Professional & scientific | 2019 |
| Stankerr (100) Limited | Real estate | 2002 |
| Stankerr (200) Limited | Real estate | 2006 |
| Stankerr Estates Limited | Real estate | 2002 |
| Stankerr Limited | Real estate | 2002 |
| Stankerr Pubs Limited | Construction | 2009 |
| Stano Consultancy Ltd | Professional & scientific | 2025 |
| Stapleton-Smith Ltd | Administrative & support | 2003 |
| Starfire Productions Limited | Administrative & support | 2013 |
| Starling Consultancy Ltd | Professional & scientific | 2011 |
| Starling CS Limited | Professional & scientific | 2016 |
| Starstruk Ltd | Professional & scientific | 2024 |
| Stay International Ltd | Hospitality | 2019 |
| Stealth Martial Arts Limited | Education | 2024 |
| Steel Frame Building Systems Limited | Wholesale & retail | 2024 |
| Steel Ready Group Limited | Construction | 2026 |
| Steelcon Services Limited | Construction | 2015 |
| Steelescale Ltd | Professional & scientific | 2025 |
| Stella Reef Ltd | Wholesale & retail | 2021 |
| Stellar Property Investment Ltd | Real estate | 2020 |
| Stellprop Limited | Hospitality | 2012 |
| Stereoscope Limited | Professional & scientific | 2019 |
| Sterling | | 2001 |
| Stobart Rigging Limited | Construction | 2023 |
| Stock Plastic Profiles Limited | Extraterritorial | 2011 |
| Stockbrook Capital Limited | Information & communication | 2017 |
| Stone Grange Mechanical Services Limited | Construction | 2018 |
| Stonebridge Crest Limited | Real estate | 2025 |
| Stoneman Property Limited | Real estate | 2015 |
| Storied Communication Limited | Professional & scientific | 2021 |
| Stormking Investments Ltd | Professional & scientific | 2019 |
| Storya Limited | Information & communication | 2018 |
| Straightforward Office Solutions Ltd | Information & communication | 2019 |
| Strategic Acquisitions Limited | Real estate | 2024 |
| Strategic Allies Limited | Professional & scientific | 2005 |
| Strategic Strategies UK Ltd | Information & communication | 2025 |
| Strategy Management Consultants Ltd | Professional & scientific | 2018 |
| Stratton Pest Control Limited | Administrative & support | 2023 |
| Stratus Recruitment International Limited | Administrative & support | 2016 |
| Straw Innovations Ltd | Water & waste | 2016 |
| Street Food Heroes Ltd | Hospitality | 2022 |
| Striving for Potential Achievement and Resilience in Kids Ltd. | Education | 2024 |
| Structure Project Management Ltd | Professional & scientific | 2020 |
| Structuresource Ltd. | Information & communication | 2009 |
| Studio Four Four Limited | Information & communication | 2009 |
| Studio L76 Ltd | Professional & scientific | 2021 |
| Studio Tinto Limited | Information & communication | 2012 |
| Sub@Omic Limited | Administrative & support | 2006 |
| Subclassic Limited | Information & communication | 2014 |
| Subconhub Ltd | Information & communication | 2026 |
| Sublimit Ltd | Wholesale & retail | 2026 |
| Suburbia Lettings Limited | Real estate | 2006 |
| Sugarox Limited | Professional & scientific | 2018 |
| Sun Lane Trading Ltd | Wholesale & retail | 2018 |
| Sunder Clothing Ltd | Wholesale & retail | 2024 |
| Sundo Limited | Real estate | 2008 |
| Sunrise Marine Ltd | Manufacturing | 2020 |
| Sunset Films Limited | Information & communication | 2015 |
| Sunshine Investment Group Limited | Real estate | 2020 |
| Superb Consulting Limited | Real estate | 2022 |
| Superdog Natural Ltd | Wholesale & retail | 2023 |
| Supporting Ltd | Wholesale & retail | 2020 |
| Sureau Ltd | Construction | 2005 |
| Surgical Vision Limited | Professional & scientific | 1994 |
| Sustainability Made Easy Limited | Professional & scientific | 2014 |
| Sustainable Citizen Labs Ltd | Information & communication | 2022 |