| Simra Mobile Accessories Ltd | Wholesale & retail | 2017 |
| Simrose Smile Ltd | Health & social care | 2022 |
| Simson Pharma Global Ltd | Professional & scientific | 2025 |
| Simt Retail Ltd | Wholesale & retail | 2018 |
| Simttec Ltd | Wholesale & retail | 2023 |
| Sinag Consulting Ltd | Professional & scientific | 2025 |
| Sincere Education & Cultural Development Limited | Education | 2017 |
| Sinclair Consultancy Ltd | Professional & scientific | 2017 |
| Sindbad Travel Ltd | Transport & logistics | 2006 |
| Sinequanon Enterprise Ltd | Administrative & support | 2025 |
| Singh & Kaur Investments Ltd | Real estate | 2019 |
| Singh & Sons London Limited | Other services | 2017 |
| Singh Power Limited | Information & communication | 2016 |
| Singing Bowl Limited | Information & communication | 2014 |
| Singularis Capital LLP | | 2024 |
| Sinhaz Limited | Health & social care | 2016 |
| Sinope Tech Ltd | Information & communication | 2024 |
| Sinpat Ltd | Real estate | 2026 |
| Sintali Ltd | Other services | 2020 |
| Siobhan Browne Ltd | Professional & scientific | 2016 |
| Sioux Limited | Financial services | 1996 |
| SIP Services Europe Limited | Information & communication | 2004 |
| Sira Property Investment Ltd | Real estate | 2026 |
| Siri IT Services Ltd | Information & communication | 2022 |
| Siri Pharma Consultancy Ltd | Information & communication | 2025 |
| Siri Tech Limited | Administrative & support | 2014 |
| Siriussoft Limited | Information & communication | 2018 |
| Sirohi Breen Consulting Ltd | Health & social care | 2014 |
| Sirsi Limited | Information & communication | 1990 |
| SIS Property Developers Ltd | Real estate | 2021 |
| Sisl Infotech (UK) Ltd | Transport & logistics | 2018 |
| Sistem Fire Ltd | Administrative & support | 2026 |
| Sister Harriet Management Limited | Households | 2005 |
| Sister's Kitchen Ltd | Hospitality | 2025 |
| Sisters & Co Cleaning Limited | Administrative & support | 2025 |
| Sisu Consultancy Ltd | Professional & scientific | 2020 |
| Sita Global Mining Opportunities, LP | | 2017 |
| Site Equipment Hire Ltd | Administrative & support | 2019 |
| Sitechiefs Ltd | Information & communication | 2022 |
| Sitrade Commodities Ltd | Wholesale & retail | 2018 |
| Siworks Ltd | Information & communication | 2023 |
| SIX 4 Forty SIX RTM Company Limited | Real estate | 2004 |
| SIX Cubes Ltd | Administrative & support | 2013 |
| SIX Planes Ltd | Information & communication | 2014 |
| Sixth MAN Advisory Limited | Professional & scientific | 2026 |
| Sixtu Ltd | Wholesale & retail | 2019 |
| Sixty Eaton Rise Limited | Real estate | 2012 |
| Sixty Eaton Rise Management Limited | Real estate | 2018 |
| Sixty-Nine Lexham Gardens Limited | Households | 1963 |
| Siya (UK) Ltd | Other services | 2013 |
| Siya Enterprise Ltd | Administrative & support | 2011 |
| Siyla Limited | Real estate | 2022 |
| Siza Group Ltd | Financial services | 2026 |
| Siza Trading Ltd | Professional & scientific | 2026 |
| Sizzle N Fizzle Limited | Hospitality | 2024 |
| Sizzlezzz Ltd | Hospitality | 2024 |
| SJ Assets Limited | Real estate | 2022 |
| SJ Broadcast Ltd | Other services | 2022 |
| SJ Education Consultancy Ltd | Education | 2024 |
| SJ Professional Decorating Services Ltd | Construction | 2025 |
| SJD Umoja Limited | Households | 2025 |
| SJG Projects Limited | Professional & scientific | 2012 |
| SJH Food Safety Consultancy Ltd | Professional & scientific | 2019 |
| SJL Global Limited | Professional & scientific | 2018 |
| SK Assets Limited | Professional & scientific | 2014 |
| SK Buildersgroup Ltd | Construction | 2018 |
| SK Concept Studio Ltd | Professional & scientific | 2025 |
| SK HR Consultancy Ltd | Administrative & support | 2019 |
| SK Legacy Ltd | Professional & scientific | 2023 |
| SK Property & Wealth Ltd | Real estate | 2025 |
| SK Property Investing Ltd | Real estate | 2024 |
| SK Security Services Ltd | Administrative & support | 2018 |
| SK Smart Solutions Ltd | Professional & scientific | 2014 |
| SK Travelss Ltd | Transport & logistics | 2022 |
| SK2 Fashion Limited | Wholesale & retail | 1996 |
| Skafa Consulting Limited | Information & communication | 2025 |
| Skalchev Ltd | Construction | 2018 |
| Skanda Accountants Ltd | Professional & scientific | 2022 |
| Skanda Vale Limited | Professional & scientific | 2016 |
| SKB Tax Services Limited | Professional & scientific | 2019 |
| SKC Experts Limited | Professional & scientific | 2013 |
| Skca Limited | Professional & scientific | 2014 |
| Skelecom Ltd | Information & communication | 2017 |
| Skentelbery Financial Planning Limited | Professional & scientific | 2023 |
| Skevel Ltd | Information & communication | 2018 |
| Skill Capital Holdings Limited | Professional & scientific | 2006 |
| Skill Capital LLP | | 2008 |
| Skillcapital Advisory LLP | | 2009 |
| Skilling Enterprise Limited | Education | 2015 |
| Skillnet Limited | Administrative & support | 2002 |
| Skillnet Training Limited | Professional & scientific | 2013 |
| Skills for Security Limited | Education | 2002 |
| Skills for Security Recruitment Limited | Education | 2002 |
| Skillsfor Holdings Ltd | Education | 2022 |
| Skillsfor Ltd | Education | 1990 |
| Skim Communications Ltd | Professional & scientific | 2025 |
| Skin & Smiles Ltd | Education | 2012 |
| Skin Citys Tattoo Company Ltd | Other services | 2013 |
| Skin Discovery Ltd | Other services | 2024 |
| Skinology Medical Aesthetics Ltd | Health & social care | 2025 |