| SHS Housing Ltd | Real estate | 2025 |
| SHU Sushi Ltd | Hospitality | 2025 |
| Shuer Home Ltd | Wholesale & retail | 2025 |
| Shuttersco Ltd | Other services | 2021 |
| Shuttleworth Landscapes Limited | Construction | 2003 |
| Shuza Limited | Wholesale & retail | 2024 |
| Shyam Raithatha Consulting Limited | Professional & scientific | 2025 |
| SI Transport and Recovery Ltd | Transport & logistics | 2023 |
| Siah Trading Co. Ltd | Wholesale & retail | 2025 |
| Sian Consulting London Ltd | Information & communication | 2025 |
| Siara Zaman Ltd | Hospitality | 2024 |
| Siaram Properties Limited | Construction | 2023 |
| Siaval Ltd | Other services | 2018 |
| SIB Services Ltd | Construction | 2020 |
| Sibs Civils Contracting Limited | Construction | 2019 |
| Sicknote Limited | Professional & scientific | 2002 |
| Sidak Haulage Ltd | Transport & logistics | 2022 |
| Sidak Transport Limited | Transport & logistics | 2021 |
| Sidbee Limited | Wholesale & retail | 2022 |
| Sidco Propco Ltd | Real estate | 2024 |
| Siddicorp Ltd | Information & communication | 2017 |
| Siddiqui & BRO Ltd | Manufacturing | 2013 |
| Sidhav Limited | Financial services | 2022 |
| Sidhs Media and Consultancy Ltd | Administrative & support | 2011 |
| Sidhu (UK) Limited | Transport & logistics | 2007 |
| Sidhu Car Audio Ltd | Wholesale & retail | 2024 |
| Sidhu Concrete and Pump Hire Ltd | Manufacturing | 2025 |
| Sidhu Daughters Properties Ltd | Real estate | 2026 |
| Sidhu Transport Management Limited | Administrative & support | 2023 |
| Sidnovate Ltd | Information & communication | 2025 |
| Sieera Ltd | Real estate | 2022 |
| Sieera Transport Ltd | Transport & logistics | 2026 |
| Siege Fire Systems Limited | Construction | 2013 |
| Sift Clean Ltd | Professional & scientific | 2023 |
| Sigma 11 Services Ltd | Wholesale & retail | 2024 |
| Sigma Cars Slough Ltd | Wholesale & retail | 2024 |
| Sigma Scaffolding Ltd | Construction | 2026 |
| Sigma Square Limited | Information & communication | 2025 |
| Signature AV Services Ltd | Arts & recreation | 2011 |
| Signature ERA Ltd | Wholesale & retail | 2026 |
| Signature Finance Ltd | Financial services | 2025 |
| Signature Network UK Ltd | Financial services | 2026 |
| Signature S Solutions Ltd | Administrative & support | 2024 |
| Signature Search Holdings Ltd | Real estate | 2020 |
| Signature Search Investments Limited | Real estate | 2016 |
| Signature Search Ltd | Financial services | 2013 |
| Signature Search Properties Ltd | Real estate | 2020 |
| Signature Search Real Estate Ltd | Real estate | 2013 |
| Signverbial Ltd | Professional & scientific | 2023 |
| Sikh Academies Trust | Education | 2020 |
| Sikh Property Limited | Real estate | 2020 |
| Sikka International Ltd | Manufacturing | 2015 |
| Sikka Pharma Ltd | Wholesale & retail | 2023 |
| Silent Film Ltd | Information & communication | 2024 |
| Silenzebeats Ltd | Wholesale & retail | 2026 |
| Silicate Ltd | Financial services | 2024 |
| Silicon Marketing Limited | Administrative & support | 2011 |
| Silikontech Limited | Information & communication | 2013 |
| Silky Shine Limited | Other services | 2025 |
| Silkyglass Limited | Wholesale & retail | 2022 |
| Silver Avenue Ltd | Hospitality | 2013 |
| Silver Leaf Housing Ltd | Other services | 2025 |
| Silver Property Investments Ltd | Real estate | 2026 |
| Silver ROW Limited | Real estate | 2023 |
| Silverah Ltd | Wholesale & retail | 2025 |
| Silvergate Properties Ltd | Real estate | 2025 |
| Silverhands Healthcare Limited | Health & social care | 2024 |
| Silverleigh Cedars Care Limited | Health & social care | 2019 |
| Silverline Entertainment Ltd | Arts & recreation | 2025 |
| Silverline Property Investments Limited | Real estate | 2020 |
| Silverline Supply Ltd | Wholesale & retail | 2026 |
| Silverstone Traders Ltd | Construction | 2025 |
| Simarj Investments Ltd | Real estate | 2020 |
| Simasiv Ltd | Transport & logistics | 2021 |
| Simaxis Ltd | Professional & scientific | 2025 |
| Simba Works Ltd | Administrative & support | 2026 |
| Simban 1313 Limited | Real estate | 2025 |
| Simetco Limited | Administrative & support | 2017 |
| Simmar Limited | Transport & logistics | 2024 |
| Simmy Solutions Ltd | Information & communication | 2024 |
| Simon & Co LLP | | 2012 |
| Simon Mwangi Ltd | Wholesale & retail | 2025 |
| Simon, Kucher & Partners Strategy & Marketing Consultants Limited | Professional & scientific | 2001 |
| Simon-Kucher Engine Ltd | Information & communication | 2021 |
| Simple Beauty & Lashes Ltd | Other services | 2018 |
| Simple Wheels Ltd | Wholesale & retail | 2022 |
| Simplified Housing Ltd | Real estate | 2019 |
| Simploo Waterless Toilets Ltd | Wholesale & retail | 2021 |
| Simply a LA Carte Ltd | Manufacturing | 2013 |
| Simply a V Ltd | Manufacturing | 2008 |
| Simply Carpet Fitters Ltd | Construction | 2025 |
| Simply Ethical Financial Services Ltd | Financial services | 2009 |
| Simply Food Solutions Limited | Manufacturing | 1993 |
| Simply Giving Foundation Ltd | Health & social care | 2025 |
| Simply Training Ltd | Professional & scientific | 2019 |
| Simplypuree.Com Ltd | Manufacturing | 2007 |
| Simplz Ltd | Wholesale & retail | 2024 |
| Simpson Demolition Services Ltd | Professional & scientific | 2026 |
| Simran Sanghera Hairstylist Ltd | Other services | 2025 |
| Simrans Collection Limited | Wholesale & retail | 2017 |