| SIM and LEE LLP | | 2014 |
| Simco Homes (Tool Watch App) Limited | Financial services | 2025 |
| Simon Beattie Ltd | Wholesale & retail | 2014 |
| Simplant Ltd | Health & social care | 2015 |
| Simply Bridget Limited | Hospitality | 2022 |
| Simply by Nature Limited | Wholesale & retail | 2015 |
| Single Horse Properties Limited | Extraterritorial | 1991 |
| Sisco Solutions Limited | Professional & scientific | 1997 |
| Sissinghurst Wines Ltd | Wholesale & retail | 2015 |
| Siteforce Recruitment Ltd | Administrative & support | 2025 |
| SK Interiors (UK) Limited | Administrative & support | 2007 |
| Skalding Ltd | Information & communication | 2024 |
| Skin Surgery Associates of London Limited | Health & social care | 2009 |
| Skinthetics Stony Stratford Ltd | Other services | 2022 |
| Sky Advisory Services Limited | Professional & scientific | 2023 |
| Skyline Project Solutions Ltd | Construction | 2021 |
| SL Consulting Group Ltd | Information & communication | 2023 |
| SL London Design Company Ltd | Professional & scientific | 2024 |
| Slad Solutions Ltd | Administrative & support | 2024 |
| Sloweyoga Limited | Education | 2025 |
| SLR Secure Consulting Ltd | Information & communication | 2011 |
| Smaart Digit Limited | Information & communication | 2016 |
| Smaart Properties Limited | Real estate | 2024 |
| Smart & Webster Limited | Information & communication | 2000 |
| Smartbrain Recruitment and Training Ltd | Health & social care | 2022 |
| Smarter Homes South Ltd | Administrative & support | 2018 |
| SMD Contract Consulting Limited | Construction | 2013 |
| Smeo Properties Ltd | Real estate | 2020 |
| Smeo Services Ltd | Information & communication | 2016 |
| Smudger Labs Ltd | Information & communication | 2025 |
| Snells Farm Limited | Real estate | 2017 |
| Snow Developments Limited | Administrative & support | 2024 |
| SNV Group Ltd | Financial services | 2023 |
| Society for Mucopolysaccharide Diseases | Professional & scientific | 2011 |
| Solada LLP | | 2021 |
| Solid Solutions Limited | Information & communication | 2007 |
| Sonal Haria Limited | Professional & scientific | 2022 |
| Sonder SET Design Limited | Professional & scientific | 2024 |
| Sophie Powell Limited | Professional & scientific | 2018 |
| Souit Consult Limited Limited | Manufacturing | 2024 |
| Soul Search Collective CIC | Arts & recreation | 2026 |
| Soul Search Finance Ltd | Health & social care | 2026 |
| Sound Crown Promotions Limited | Arts & recreation | 2019 |
| SP Tech Partners Ltd | Information & communication | 2025 |
| Spacecode Ltd | Professional & scientific | 2026 |
| Spare Pixels Ltd | Extraterritorial | 2022 |
| Sparkle DRY Cleaners Ltd | Other services | 2024 |
| Sparkls Property Limited | Real estate | 2017 |
| Speller Surveying Limited | Professional & scientific | 2021 |
| Spice of Amersham Ltd | Hospitality | 2019 |
| Spigs Limited | Other services | 2023 |
| Spinney Place Ltd | Households | 2020 |
| Spinning-Gold Ltd | Professional & scientific | 2012 |
| Spoke 42 Limited | Information & communication | 2021 |
| Spondulix Ltd | Professional & scientific | 2023 |
| Sports Vectors Ltd | Information & communication | 2026 |
| Springmere Limited | Professional & scientific | 2000 |
| Springsong Limited | Administrative & support | 1999 |
| Spss Innovations Ltd | Professional & scientific | 2025 |
| Spuddy Macs Ltd | Hospitality | 2026 |
| Spurr Consulting Limited | Professional & scientific | 2022 |
| Squad Four Limited | Information & communication | 2014 |
| Square Mile Limited | Professional & scientific | 2024 |
| Squirrel Thames Valley Limited | Real estate | 1999 |
| SRC Recruitment Limited | Administrative & support | 2014 |
| SRE Solutions Ltd | Professional & scientific | 2015 |
| SRI Laxmi Narasimha Swamy Trading Ltd | Wholesale & retail | 2023 |
| Srushti Renewables Ltd | Financial services | 2023 |
| SS Technology Consultancy Limited | Professional & scientific | 2023 |
| SSR IT Ltd | Professional & scientific | 2017 |
| ST Filling Station Ltd | Wholesale & retail | 2020 |
| ST Mary's Boxmoor Developments Limited | Administrative & support | 2014 |
| ST Vincent Reserve (UK) General Partner Limited | Administrative & support | 2006 |
| ST Vincent Reserve (UK) LP | | 2008 |
| ST. James Interiors Ltd | Administrative & support | 2016 |
| ST. James Joinery London Ltd | Manufacturing | 2010 |
| ST. John's Court Management (Warwick) Limited | Households | 1978 |
| ST. Nicholas Holmes Limited | Construction | 2010 |
| Stackbourne Developments Limited | Construction | 2023 |
| Stage 2 Screen Construction Limited | Construction | 2016 |
| Starlight Fireworks Limited | Professional & scientific | 1990 |
| Statsconsultancy Limited | Professional & scientific | 2008 |
| Stayarc.Com Ltd | Information & communication | 2025 |
| Stella Logistics Limited | Extraterritorial | 2019 |
| Step UP Physiotherapy and Rehabilitation Ltd | Health & social care | 2014 |
| Stephenson Wharf Associates Limited | Households | 2021 |
| Sterling United Limited | Real estate | 2026 |
| Steven Rosenthal Estate Agent Ltd | Real estate | 2023 |
| Stilton Investments Limited | Real estate | 2022 |
| Stirling Cumming Global Ltd | Professional & scientific | 2024 |
| Stirling Cumming Gregory Ltd | Real estate | 2024 |
| Storage West Basildon Ltd | Real estate | 2024 |
| Storage West Cheltenham Ltd | Real estate | 2026 |
| Storage West Group Ltd | Financial services | 2026 |
| Storyland Locations Limited | Construction | 2025 |
| Storyland Studios Ltd | Professional & scientific | 2020 |
| Strategic Brief Limited | Professional & scientific | 2002 |
| Strategic Transportation Ltd | Transport & logistics | 2018 |
| Strategically People Limited | Professional & scientific | 2021 |
| Stratos Group Ltd | Administrative & support | 2023 |