| SEJ Global Ltd | Information & communication | 2025 |
| Selfbuild Solutions Limited | Construction | 2000 |
| Selfbuild Solutions.Com Limited | Construction | 2000 |
| Send and Receive Limited | Administrative & support | 2010 |
| Sendall Consultancy Ltd | Information & communication | 2021 |
| Sendoa Services Ltd | Information & communication | 2015 |
| Sequence (UK) Limited | Financial services | 2001 |
| Sequencing Ltd | Real estate | 2021 |
| Serendipity Stays Limited | Real estate | 2025 |
| Sergeant Communications Limited | Professional & scientific | 2016 |
| Servpro Limited | Extraterritorial | 2013 |
| Seso Property Limited | Real estate | 2020 |
| Seso Solutions Ltd | Information & communication | 2016 |
| Seso Staffing Ltd | Health & social care | 2022 |
| SET the Scene Limited | Professional & scientific | 2000 |
| Sethi Properties Limited | Real estate | 2017 |
| Seven Gables RTM Company Limited | Households | 2015 |
| Seven Profiles Limited | Information & communication | 2024 |
| Sevro Groundcare Ltd | Administrative & support | 2023 |
| SF Psychology Limited | Health & social care | 2023 |
| SG Copywriting Ltd | Professional & scientific | 2017 |
| SGC Interiors Limited | Construction | 2009 |
| SGE Holdings Limited | Construction | 2019 |
| SGM Controls Ltd. | Manufacturing | 2005 |
| SH Machinerepair Ltd | Manufacturing | 2025 |
| Shahz Cars Ltd | Wholesale & retail | 2020 |
| Share Moss Group Limited | Wholesale & retail | 2025 |
| Share Your Mindset Limited | Wholesale & retail | 2019 |
| Sharman Quinney Holdings Limited | Financial services | 2001 |
| Sharp's Transport (Leighton Buzzard) Limited | Transport & logistics | 2012 |
| Shaw Property Investment Co Ltd | Real estate | 2013 |
| Shazi Store Ltd | Wholesale & retail | 2025 |
| Shazia Consulting Limited | Administrative & support | 2024 |
| Shcoh Ltd | Professional & scientific | 2019 |
| Sheep Shed Creations Ltd | Construction | 2022 |
| Shenley Court (Freehold) Limited | Households | 2011 |
| Shepherd Street Limited | Real estate | 2024 |
| Shiba Dog Studios Limited | Information & communication | 2024 |
| Shimmtek Limited | Information & communication | 2010 |
| Shnordic Ltd | Education | 2023 |
| Shopanix Ltd | Wholesale & retail | 2025 |
| Shoptownukpl Ltd | Wholesale & retail | 2022 |
| Short Legged Roofing Limited | Construction | 2025 |
| Sian Wilde Limited | Wholesale & retail | 2024 |
| Sidash Limited | Professional & scientific | 2013 |
| Siecle Velo Limited | Manufacturing | 2025 |
| Sight Unseen Productions Limited | Professional & scientific | 2016 |
| Sightline Windows Ltd | Construction | 2024 |
| Signature Luxe Limited | Wholesale & retail | 2025 |
| Signature Packaging Limited | Wholesale & retail | 2018 |
| Silva Delivers Limited | Transport & logistics | 2017 |
| Silver City Airways Ltd. | Transport & logistics | 1999 |
| Silver FOX Sports Ltd | Arts & recreation | 2021 |
| Silver Spear Debt Management Ltd | Financial services | 2020 |
| Silverback Consultancy Limited | Professional & scientific | 2022 |
| Silverfoxx Associates Limited | Professional & scientific | 2025 |
| Silverplank Logis Ltd | Manufacturing | 2016 |
| Sima Asphalt Limited | Professional & scientific | 2016 |
| Sima Environment Ltd | Professional & scientific | 2021 |
| Simmons Site Sevices Ltd | Construction | 2025 |
| Simon Blott Scientific Services Ltd | Professional & scientific | 2023 |
| Simon Tibbs Ltd | Information & communication | 2013 |
| Simplabs Limited | Professional & scientific | 2020 |
| Simplify Technology Services Limited | Information & communication | 2021 |
| Simply Electrical Services Ltd | Construction | 2011 |
| Simply Land & Property Ltd | Construction | 2023 |
| Simpson Hance Group Ltd | Construction | 2017 |
| Simril Solutions Ltd | Information & communication | 2025 |
| Sinclair Leask Limited | Professional & scientific | 2010 |
| Sinukri Healthcare Ltd | Health & social care | 2024 |
| SIO Logistics Limited | Transport & logistics | 2024 |
| Sistermatic Cleaning Ltd | Administrative & support | 2022 |
| Sisu Solutions Ltd | Professional & scientific | 2018 |
| Site Office Services Ltd | Professional & scientific | 2026 |
| Situnes Limited | Information & communication | 2020 |
| SIX Star Events Ltd | Arts & recreation | 2024 |
| Sizzler Leighton Limited | Hospitality | 2025 |
| SJC Conveyancing Ltd | Other services | 2023 |
| Sjeza Logistics Ltd | Transport & logistics | 2019 |
| SJG SET Solutions Limited | Construction | 2024 |
| SK Compliance and Fire Risk Assessor Ltd | Public administration | 2017 |
| SK Luton Ltd | Hospitality | 2025 |
| SK Movies Ltd | Information & communication | 2021 |
| Skilled Staff Direct Limited | Administrative & support | 2025 |
| Skin Health Solutions Ltd | Wholesale & retail | 2016 |
| SKS Plumbing Services Limited | Construction | 2012 |
| SLA Smile Care Limited | Health & social care | 2025 |
| Slimson Limited | Wholesale & retail | 2021 |
| SM Design & Consulting Limited | Administrative & support | 2018 |
| Small Steps Big Change Ltd | Health & social care | 2022 |
| Smallglen Limited | Construction | 1972 |
| Smart Choice Healthcare Ltd | Health & social care | 2020 |
| Smart Criminal Defence Ltd | Professional & scientific | 2021 |
| Smart Frog Ltd | Professional & scientific | 2006 |
| Smart Property Inventories Ltd | Real estate | 2021 |
| Smart Start Cars Ltd | Wholesale & retail | 2026 |
| Smarter Transport Consulting Limited | Transport & logistics | 2023 |
| Smartux Ltd | Information & communication | 2019 |
| Smashing Agile Ltd | Information & communication | 2022 |
| Smashing Sets Limited | Construction | 2019 |