| S2 Analytics Ltd | Information & communication | 2025 |
| Sabre H&S Ltd | Public administration | 2023 |
| Sacred Fade Ltd | Other services | 2025 |
| Sadie and Franks Nursery Limited | Other services | 2018 |
| Saecom Ltd | Information & communication | 2014 |
| Safe Demolition & Dismantling Services Limited | Construction | 2016 |
| Safe Hands Aesthetics Ltd | Health & social care | 2022 |
| Safe Roots Cymru C.I.C. | Other services | 2025 |
| Safeguard Home Improvements Limited | Construction | 2019 |
| Safeguard Security Solutions Ltd | Administrative & support | 2025 |
| Safely Construct Limited | Professional & scientific | 2025 |
| Safer Aesthetics Training Ltd | Health & social care | 2022 |
| Safety at Work Ltd | Professional & scientific | 2005 |
| Safron Locum Limited | Administrative & support | 2025 |
| Sage Foods Ltd | Extraterritorial | 2017 |
| Saint Davids Fire Ltd | Other services | 2024 |
| Saitbaba Ltd | Hospitality | 2024 |
| Salar Environmental Services Ltd | Professional & scientific | 2019 |
| Sales Revolution UK Ltd | Administrative & support | 2023 |
| Salmata Foods Ltd | Hospitality | 2026 |
| Salon Loulou Limited | Other services | 2017 |
| Salvataggio Dati Limited | Information & communication | 2008 |
| SAM Security Limited | Administrative & support | 2024 |
| SAM Vincent Designs Ltd | Information & communication | 2023 |
| Sama Shams Limited | Other services | 2025 |
| Samahan Properties Limited | Real estate | 2021 |
| Samar Ciao Limited | Professional & scientific | 2024 |
| Samdell Cleaning Services Ltd | Administrative & support | 2022 |
| Samsons Cash & Carry Limited | Wholesale & retail | 2009 |
| Samuel Thomas Limited | Construction | 2019 |
| Sandcade Limited | Extraterritorial | 2026 |
| Sandform Limited | Extraterritorial | 2026 |
| Sandpit Properties Ltd | Real estate | 2025 |
| Sandport Limited | Extraterritorial | 2025 |
| Sano Marketing Ltd | Financial services | 2017 |
| Sapphire ESG Ltd | Construction | 2021 |
| SAR & NY Limited | Wholesale & retail | 2022 |
| Sara Building Services Limited | Construction | 2025 |
| Sarah Family Homes Ltd | Real estate | 2018 |
| Sarah Ratcliffe Limited | Professional & scientific | 2008 |
| Sardeep Singh Ltd | Wholesale & retail | 2025 |
| Sarla-Uk CYF | Information & communication | 2025 |
| Sati Services Ltd | Professional & scientific | 2019 |
| Satori Events Ltd | Arts & recreation | 2024 |
| Satori Weddings Ltd | Information & communication | 2022 |
| Saunders Properties Limited | Construction | 2009 |
| Saundstone Property Limited | Construction | 2021 |
| SAW Food Services Ltd | Hospitality | 2024 |
| SBP UK Holdings Limited | Administrative & support | 2025 |
| SBW Investments Limited | Extraterritorial | 2007 |
| Scarlet Design International Limited | Arts & recreation | 1997 |
| Scdm Transport Limited | Transport & logistics | 2018 |
| Scholarbridge Ltd | Information & communication | 2025 |
| School Governance Solutions Ltd | Administrative & support | 2015 |
| School of Healing Mastery Ltd | Education | 2021 |
| SCL Construction & Refurbishment Ltd | Construction | 2020 |
| Scor Bars Ltd | Hospitality | 2019 |
| Scott Grey Limited | Professional & scientific | 2013 |
| Scott Waste Holdings Ltd | Financial services | 2021 |
| Scott Waste Ltd | Water & waste | 2013 |
| Screed Solutions South Wales Ltd | Construction | 2023 |
| SD Electrix Ltd | Construction | 2014 |
| SDC Employee Ownership Trustee Limited | Professional & scientific | 2025 |
| SDL Fit OUT Limited | Professional & scientific | 2016 |
| SDL Interior Solutions Ltd | Construction | 2020 |
| SE Atwo Ltd | Information & communication | 2024 |
| SE Fasade Ltd | Extraterritorial | 2010 |
| Seafern Luxury Stays Limited | Real estate | 2025 |
| Sean Brightman Ltd | Information & communication | 2009 |
| Seashell Stays Pembrokeshire Ltd | Real estate | 2026 |
| Seating on Line Limited | Wholesale & retail | 1999 |
| Sebwood Products Limited | Manufacturing | 2006 |
| Secret Fantasy Entertainment Ltd | Information & communication | 2025 |
| Secret Fire Software Ltd | Information & communication | 1996 |
| Sector Development Wales Partnership Limited | Public administration | 2013 |
| Securcare Limited | Transport & logistics | 2016 |
| Secureit UK Limited | Administrative & support | 2007 |
| Sehar Consultancy Limited | Professional & scientific | 2024 |
| Sehar Holdings Limited | Financial services | 2024 |
| Sehar Property Limited | Real estate | 2024 |
| Seipec Ltd | Construction | 2016 |
| Seirian Elys Projects Limited | Professional & scientific | 2014 |
| Select Fires Limited | Wholesale & retail | 2025 |
| Select Upvc Windows Ltd | Construction | 2022 |
| Selwyn Surveying Limited | Construction | 2016 |
| Sematronix Limited | Information & communication | 2010 |
| Sematronix Technologies Limited | Information & communication | 2022 |
| SEN Farmers Limited | Hospitality | 2025 |
| Senfield Properties Limited | Real estate | 2025 |
| Senior Surveys Ltd | Professional & scientific | 2016 |
| Sensible Financial Management Ltd | Professional & scientific | 2019 |
| Sentien Group LLP | | 2026 |
| Sepsolve Analytical Limited | Manufacturing | 2002 |
| Seren Sarn Ltd | Professional & scientific | 2017 |
| Seren Virtual Production Limited | Information & communication | 2024 |
| Serenity Support and Care CIC | Health & social care | 2024 |
| Sergiu & Milan Ltd | Transport & logistics | 2023 |
| Seriously Spooky Ltd | Information & communication | 2024 |
| Service Essential Cleaning Ltd | Administrative & support | 2019 |
| Services Supply Company Limited | Wholesale & retail | 2007 |