| Sierra SAM Productions Limited | Arts & recreation | 2018 |
| Sierra UK Investments Ltd | Real estate | 2017 |
| Signature Group Holdings Limited | Financial services | 2023 |
| Signature Recruitment Bristol Limited | Administrative & support | 2010 |
| Signature Recruitment Ltd | Administrative & support | 2010 |
| Signature Resorts (UK) Limited | Construction | 2006 |
| Signature Resorts Limited | Administrative & support | 2007 |
| Silicon Roundabout Limited | Extraterritorial | 2012 |
| Siliconeman Ltd | Construction | 2019 |
| Silva Salt Ltd | Manufacturing | 2025 |
| Silver Hind Court Management Limited | Households | 2012 |
| Silverbrook Homes Ltd | Construction | 2021 |
| Silverman Sato Search and Selection Limited | Administrative & support | 2017 |
| Silverton Properties (Clements Road) Limited | Real estate | 2025 |
| Silverton Property Investments Limited | Hospitality | 1997 |
| Simam Limited | Professional & scientific | 2022 |
| Simmi Group Holdings Limited | Financial services | 2021 |
| Simmi UK Ltd | Wholesale & retail | 2012 |
| Simple Investment Solutions Limited | Real estate | 2012 |
| Simplex Maths LLP | | 2025 |
| Simply Group Services Ltd | Water & waste | 2019 |
| Simply Seafood (Epping) Ltd | Hospitality | 2025 |
| Simpson and SON Properties Ltd | Real estate | 2025 |
| Simvas Construction Ltd | Manufacturing | 2017 |
| Sinden Flooring Ltd | Construction | 2007 |
| Sinead Sheehy Chiropractic Limited | Public administration | 2024 |
| Singh and Kaur Portfolios Ltd | Real estate | 2024 |
| Singhcoin Ltd | Professional & scientific | 2018 |
| Sinm Properties Limited | Construction | 2017 |
| SIP Social Limited | Extraterritorial | 2024 |
| SIP Trustees Limited | Administrative & support | 1999 |
| Sipp'D Limited | Manufacturing | 2019 |
| Sirius Prospects Limited | Real estate | 2024 |
| Sirocco Business Solutions Ltd | Real estate | 2017 |
| Sisu Recruiting Ltd | Administrative & support | 2020 |
| Sitara Moda Ltd | Wholesale & retail | 2025 |
| Site Sales Holdings Limited | Financial services | 2024 |
| Site Sales Limited | Real estate | 2014 |
| Siteform Flooring Contractors Ltd | Construction | 2012 |
| Sitesales Property Group Limited | Real estate | 2017 |
| Sitie Smart Ltd | Wholesale & retail | 2025 |
| SIV Construction Services Ltd | Construction | 2019 |
| Sivom Limited | Real estate | 2016 |
| SIX Consultancy Limited | Administrative & support | 2018 |
| SIX Holdings Limited | Professional & scientific | 2018 |
| SJ Building Contracts Ltd | Construction | 2019 |
| SJ Hirst Limited | Professional & scientific | 2017 |
| SJC Electrical Services Ltd | Energy | 2016 |
| Sjconnolly Electrical Ltd | Construction | 2019 |
| SJK Management Ltd | Professional & scientific | 2022 |
| SJM Plastering Ltd | Construction | 2024 |
| SJS Associates (Essex) Ltd | Construction | 2016 |
| SK (London) Construction Limited | Construction | 2015 |
| SK Hollies Road Limited | Real estate | 2019 |
| SK Julien Road Limited | Real estate | 2018 |
| SKA Drylining Ltd | Construction | 2015 |
| Skarbek One Ltd | Real estate | 2023 |
| SKB Electrical Limited | Energy | 2023 |
| Skin Renew London Limited | Health & social care | 2017 |
| Skinclaire Beauty Ltd | Other services | 2023 |
| SKT Property Solutions Limited | Real estate | 2025 |
| Sktk Properties Limited | Real estate | 2020 |
| Sky Air Conditioning Limited | Energy | 2005 |
| Sky Blue Tavern Ltd | Hospitality | 2024 |
| Sky Cloud London Ltd | Information & communication | 2014 |
| Sky Exterior Cleaning Solutions Ltd | Administrative & support | 2024 |
| Sky Rope Access Ltd | Construction | 2025 |
| Skyford Trade Ltd | Wholesale & retail | 2025 |
| Skynet Computer Systems Limited | Information & communication | 1983 |
| SL Cricx Ltd | Financial services | 2019 |
| SLA Tools and Site Services Limited | Manufacturing | 2026 |
| Slhms Ltd | Real estate | 2022 |
| Slice Sourdough Pizza Limited | Hospitality | 2020 |
| Slick Construction (London) Ltd | Construction | 2016 |
| Slightly Sidewayz Ltd | Information & communication | 2025 |
| Sloane House Marketing Limited | Professional & scientific | 2022 |
| SM Emerald Property Management Ltd | Real estate | 2026 |
| SM Lucky Ltd | Wholesale & retail | 2026 |
| Smab Properties Limited | Real estate | 2025 |
| Smarrt Bookings Ltd | Administrative & support | 2024 |
| Smart Carrier Solutions Ltd | Transport & logistics | 2024 |
| Smart Casual Design Ltd | Administrative & support | 2014 |
| Smart Choice Estate Ltd | Real estate | 2019 |
| Smart D2C Marketing Ltd | Information & communication | 2025 |
| Smart Flow Engineering Ltd | Professional & scientific | 2025 |
| Smart Heathrow Parking Ltd | Wholesale & retail | 2019 |
| Smart Home and Lighting Systems Ltd | Construction | 2015 |
| Smashandhash Ltd | Hospitality | 2026 |
| SMB (Blurton Road) Limited | Real estate | 2018 |
| SMB Estates Limited | Real estate | 2006 |
| SMC Construction & Maintenance Limited | Construction | 2014 |
| Smearless Cleaning Limited | Administrative & support | 2025 |
| Smiley Faces Childcare Ltd | Health & social care | 2026 |
| Smita Verma Ltd | Wholesale & retail | 2016 |
| Smith Mcdonald & Co. Limited | Real estate | 1970 |
| Smith's of Loughton Limited | Wholesale & retail | 2003 |
| Smith's Property Limited | Real estate | 2003 |
| Smithfield (Wholesale Butchers) Limited | Wholesale & retail | 2009 |
| Smiths Electrical Group Ltd | Construction | 2025 |
| Smitp Ltd | Construction | 2025 |