| Silver Mackerel Designs Ltd | Professional & scientific | 2023 |
| Silver Stores Limited | Wholesale & retail | 2016 |
| Silver Street Cars London Limited | Wholesale & retail | 2015 |
| Silver Studios VFX Limited | Information & communication | 2016 |
| Silverback Movements Limited | Transport & logistics | 2015 |
| Silvercast Limited | Wholesale & retail | 2003 |
| Silverdome Care Ltd | Health & social care | 2016 |
| Silverdyne Systems Limited | Information & communication | 2011 |
| Silverhawk Limited | Professional & scientific | 1994 |
| Silverlane Limited | Real estate | 1982 |
| Silvermir Limited | Information & communication | 1996 |
| Silverstar Chauffeurs Ltd | Transport & logistics | 2008 |
| Silwoods Limited | Real estate | 2017 |
| Simate Limited | Information & communication | 2010 |
| Simba Estates Ltd | Real estate | 2020 |
| Simion PC Construction Limited | Construction | 2017 |
| Simon Buildings Ltd | Construction | 2021 |
| Simon Conroy Legal Ltd | Other services | 2017 |
| Simon Groom Limited | Professional & scientific | 2005 |
| Simon Latus Media Ltd | Information & communication | 2011 |
| Simon Longman Artwork Ltd | Arts & recreation | 2014 |
| Simon Ziff Limited | Other services | 2024 |
| Simone Battistella Consulting Limited | Arts & recreation | 2009 |
| Simple Solutions Services Limited | Information & communication | 2015 |
| Simpler Markets Limited | Education | 2012 |
| Simply D Best Kitchens Ltd | Wholesale & retail | 2020 |
| Simply Gracious Ltd | Hospitality | 2018 |
| Simply Smiling Ltd | Health & social care | 2017 |
| Simpsons Property Developments Limited | Real estate | 2018 |
| Simrah Enterprises Ltd | Real estate | 2025 |
| Simtrical Ltd | Professional & scientific | 2018 |
| Simy Construction Ltd | Construction | 2025 |
| Since Yesterday Limited | Professional & scientific | 2009 |
| Sinwelt Investments Ltd | Real estate | 2022 |
| Sipkube Limited | Information & communication | 2021 |
| SIS Technologies Limited | Information & communication | 2012 |
| Sisal and Seagrass Ltd | Construction | 2013 |
| Sister London Limited | Professional & scientific | 1999 |
| Sitamarhi Limited | Real estate | 2016 |
| Site Security Ltd | Administrative & support | 2012 |
| Sitek Solutions Limited | Information & communication | 2009 |
| Situnet Limited | Information & communication | 2002 |
| Siva Medical Services Ltd | Health & social care | 2016 |
| Sixtythreepointfive Limited | Manufacturing | 2025 |
| SJ Service Solutions Ltd | Construction | 2020 |
| SJD Limited | Construction | 2015 |
| SJH 24 Plumbing and Heating Ltd | Construction | 2018 |
| SJK London Limited | Professional & scientific | 2024 |
| SJP Aviation Ltd | Education | 2025 |
| SK Dental Ltd | Health & social care | 2019 |
| SK Holdings Limited | Financial services | 2016 |
| SK Property Exchange Limited | Real estate | 2026 |
| SKC Investments Limited | Real estate | 2014 |
| SKC Space CIC | Arts & recreation | 2024 |
| Skeltons Chemists Limited | Wholesale & retail | 2006 |
| Skess Ltd | Construction | 2018 |
| Skilljobs Ltd | Professional & scientific | 2021 |
| Skin Medical Clinics Limited | Health & social care | 2017 |
| Skincyclopedia Ltd | Other services | 2024 |
| Skinext Ltd | Other services | 2024 |
| Sky Creative for Trading and Contracting Ltd | Construction | 2025 |
| Skydive Centre Limited | Education | 2015 |
| Skye Properties London Ltd | Construction | 2021 |
| Skyera Ltd | Administrative & support | 2018 |
| Skyfest Limited | Arts & recreation | 2025 |
| Skylite Cleaning Ltd | Other services | 2018 |
| Skyward Ltd | Wholesale & retail | 2003 |
| SL Financial Consultancy Limited | Administrative & support | 2017 |
| SLA Global Consulting Ltd | Professional & scientific | 2010 |
| Slayedbyeki Ltd | Other services | 2026 |
| SLC14 Ltd | Administrative & support | 2018 |
| Sldc Limited | Information & communication | 2015 |
| Slfr Investments | Professional & scientific | 2025 |
| Slim Services Ltd | Information & communication | 2017 |
| Slipstructures Limited | Construction | 2016 |
| SLO SKI Consultancy Limited | Information & communication | 2003 |
| SLO Solutions Ltd | Other services | 2021 |
| Sloane 18-20 Limited | Households | 2020 |
| Sloane Psychology Limited | Health & social care | 2011 |
| SLS of Mayfair Concierge Limited | Transport & logistics | 2024 |
| SLY FOX Films Limited | Information & communication | 1982 |
| SM Cyber Solutions Ltd | Information & communication | 2023 |
| SM Investments (U.K.) Limited | Real estate | 2017 |
| Small MAN Limited | Information & communication | 2010 |
| Smart Builders North West Limited | Construction | 2016 |
| Smart Capital Group Ltd | Financial services | 2017 |
| Smart Care Nursing Agency and Transport Ltd | Transport & logistics | 2022 |
| Smart Carriers Ltd | Transport & logistics | 2009 |
| Smart Environment Holding Ltd | Financial services | 2023 |
| Smart Freight Logistics Ltd | Transport & logistics | 2017 |
| Smart Soluxions Limited | Administrative & support | 2024 |
| Smartia Ltd | Information & communication | 2018 |
| Smartos Ltd | Construction | 2022 |
| Smartway Electrical Services Limited | Construction | 2014 |
| Smartypants Productions Limited | Information & communication | 2017 |
| Smash Drop Ltd | Arts & recreation | 2026 |
| Smeuse Limited | Professional & scientific | 2026 |
| SMG Property Investments Limited | Real estate | 2014 |
| Smile & Sparkle Ltd | Other services | 2017 |
| Smile Designer Ltd | Administrative & support | 2017 |