| Seewell Limited | Professional & scientific | 2013 |
| Sef-Cymru | Education | 2010 |
| Seftobass Ltd | Arts & recreation | 2024 |
| SEG Quantity Surveying Limited | Construction | 2018 |
| Seguroxr Ltd | Information & communication | 2025 |
| SEH Property Limited | Real estate | 2015 |
| Sehar Motors Limited | Wholesale & retail | 2019 |
| Seharish Tariq Ltd | Professional & scientific | 2021 |
| Sehco Ltd | Financial services | 2020 |
| Sehr Trading Ltd | Administrative & support | 2020 |
| Seimei Consult Ltd | Information & communication | 2017 |
| Seimon LEA SFX Ltd | Other services | 2021 |
| Seinfeld Limited | Construction | 2022 |
| Seirian Limited | Health & social care | 2012 |
| Sekhon Tranport Ltd | Transport & logistics | 2026 |
| Sekolax Ltd | Other services | 2025 |
| SEL Building Corporation Limited | Construction | 2018 |
| SEL Leasing Ltd | Wholesale & retail | 2018 |
| Selachii Legal Limited | Professional & scientific | 2018 |
| SELAH139 Limited | Professional & scientific | 2023 |
| Seldons Sweets Ltd | Wholesale & retail | 2018 |
| Select Activewear Ltd | Wholesale & retail | 2025 |
| Select Coach Hire Limited | Transport & logistics | 2013 |
| Select Labour Solutions Ltd | Wholesale & retail | 2015 |
| Select Perfusion Services Limited | Health & social care | 2024 |
| Select Testing (Wales) Limited | Construction | 2008 |
| Selectbrix and Chill Ltd | Wholesale & retail | 2019 |
| Selected FEW Club Ltd | Professional & scientific | 2020 |
| Selectif Limited | Professional & scientific | 2008 |
| Selective Roofing Ltd | Construction | 2025 |
| Selecto Limited | Professional & scientific | 2019 |
| Selectrofix Ltd | Construction | 2017 |
| Selefkos Ltd | Wholesale & retail | 2026 |
| Self KG Limited | Arts & recreation | 2025 |
| Self Love Superstore Ltd | Arts & recreation | 2024 |
| Self Recruitment Construction Limited | Administrative & support | 2015 |
| Self Serv Ltd | Extraterritorial | 2018 |
| Selikya Ltd | Wholesale & retail | 2024 |
| Selimovic Ltd | Wholesale & retail | 2024 |
| Selin Iscan Ltd | Wholesale & retail | 2024 |
| Sell Ecart Limited | Wholesale & retail | 2026 |
| Sell House Fast Group Ltd | Real estate | 2020 |
| Sell My Bike! Ltd | Wholesale & retail | 2019 |
| Sell Quality Ltd | Wholesale & retail | 2025 |
| Sell, Buy OR Xchange Multi Media Online Ltd | Wholesale & retail | 2021 |
| SELL2U Limited | Wholesale & retail | 2025 |
| Sellami Limited | Administrative & support | 2019 |
| Sellerpro 360 Limited | Information & communication | 2025 |
| Sellershub AI Ltd | Wholesale & retail | 2025 |
| Sellify Ecom Ltd | Wholesale & retail | 2025 |
| Selling Solution One Ltd | Construction | 2020 |
| Sellmore Ltd | Information & communication | 2021 |
| Sello Beauty Ltd | Wholesale & retail | 2025 |
| Sellogy Ltd | Wholesale & retail | 2025 |
| Sellora Digital Ltd | Information & communication | 2025 |
| Sellstyle Ltd | Other services | 2025 |
| Selluxsky LLP | | 2025 |
| Selly Park Curry Cottage Ltd | Hospitality | 2015 |
| Selm Properties Limited | Real estate | 2016 |
| Selskar Solutions Limited | Administrative & support | 2021 |
| Seltd Realisations Limited | Manufacturing | 1966 |
| Seltreks Business Ltd | Wholesale & retail | 2025 |
| Selvium Healthcare Ltd | Manufacturing | 2025 |
| Semacol Enterprises Limited | Mining & quarrying | 2011 |
| Semantics MR Limited | Professional & scientific | 2009 |
| Semaphore (Cardiff) Limited | Professional & scientific | 1985 |
| Semfa International Limited | Professional & scientific | 1984 |
| Semi MED Thermal Ltd | Professional & scientific | 2024 |
| Semich Ltd | Health & social care | 2020 |
| Semihvintage Ltd | Wholesale & retail | 2025 |
| Seminal Limited | Real estate | 2003 |
| Semlec Ltd | Construction | 2021 |
| Semper Amaraye Limited | Wholesale & retail | 2021 |
| Sempex International Limited | Wholesale & retail | 2015 |
| Sems Medical Services Ltd | Health & social care | 2017 |
| SEN Bread Limited | Manufacturing | 2019 |
| SEN Globe Ltd | Professional & scientific | 2021 |
| SEN Wrld Ltd | Wholesale & retail | 2025 |
| Sencix Ltd | Information & communication | 2025 |
| Senco Technology Ltd | Extraterritorial | 2019 |
| Send DM Limited | Administrative & support | 2020 |
| Send-Ar Ltd | Construction | 2015 |
| Sendam Digital Technology Limited | Information & communication | 2022 |
| Senday Brogan Consulting Ltd | Professional & scientific | 2025 |
| Sendero Collective Limited | Information & communication | 2026 |
| Sene Group PC | | 2017 |
| Seneca Direct Ltd | Construction | 2016 |
| Seneca Group Holdings Ltd | Wholesale & retail | 2012 |
| Seneste Ltd | Wholesale & retail | 2021 |
| Senger Consultancy Ltd | Wholesale & retail | 2025 |
| Senghani Father & SON Commercial Ltd | Households | 2025 |
| Senghani Father & SON Homes Ltd | Real estate | 2022 |
| Senghennydd Road Management Company Ltd | Households | 2001 |
| Sengul Koyuncu Ltd | Wholesale & retail | 2025 |
| Senility Ltd | Information & communication | 2025 |
| Seninn Ltd | Wholesale & retail | 2026 |
| Senkoa Ltd | Wholesale & retail | 2023 |
| Senmuk TV Limited | Information & communication | 2021 |
| Senna Construction Services Limited | Construction | 2022 |
| Sensa Atlantis International Ltd | Financial services | 2019 |