| S D M C Law Limited | Professional & scientific | 2006 |
| S Jones Consulting Limited | Information & communication | 2016 |
| S K Retailers Ltd | Wholesale & retail | 2023 |
| S&G Taxis Limited | Transport & logistics | 2026 |
| S. I. Evans and SON Limited | Real estate | 1979 |
| S.M.D. Legal Consultancy Limited | Professional & scientific | 2019 |
| SA Mechanical Fitting Ltd | Professional & scientific | 2025 |
| SA Utility Services Limited | Construction | 2021 |
| SA1 Interior Design Ltd | Professional & scientific | 2024 |
| SA15 Car Sales Ltd. | Wholesale & retail | 2018 |
| SA15 Stage School Limited | Arts & recreation | 2018 |
| Saba Consult Holdings Limited | Professional & scientific | 2025 |
| Sabai KA Ltd | Transport & logistics | 2019 |
| Sabre Ecological Services Ltd | Professional & scientific | 2022 |
| Safe Hands Security & Events Services Ltd | Water & waste | 2025 |
| Safe Hands Security Ltd | Administrative & support | 2017 |
| Safe Storage Space Ltd | Transport & logistics | 2025 |
| Sage Home Developments Ltd | Construction | 2024 |
| Salem Films Limited | Information & communication | 2000 |
| Sali J Properties Ltd | Real estate | 2018 |
| Salon B Ltd | Other services | 2008 |
| SAM Davies Property Ltd | Construction | 2025 |
| SAM Kurdish Barber Cross Hands Ltd | Other services | 2024 |
| SAM Stubbins Ltd | Wholesale & retail | 2025 |
| Samrah Buddsoddiadau Cyfyngedig | Professional & scientific | 2020 |
| Samuels Developments Limited | Construction | 2020 |
| Sanderson Drake Group Ltd | Financial services | 2024 |
| Sanderson Drake Limited | Professional & scientific | 2017 |
| Sandhey Estates Limited | Real estate | 2025 |
| Sandhey Stores Limited | Wholesale & retail | 2018 |
| Sandy Road Filling Station Ltd | Wholesale & retail | 2018 |
| Sandygate Associates Limited | Professional & scientific | 2015 |
| Sanshirokwai Ltd | Arts & recreation | 2022 |
| Santa's Spirits Ltd | Manufacturing | 2023 |
| Sasha Grant Financial Services Ltd | Financial services | 2010 |
| Satori Martial Arts Academy Ltd | Education | 2023 |
| Sattnav Limited | Hospitality | 2020 |
| Sauro Homes Limited | Construction | 2002 |
| SAZ Accountancy Limited | Professional & scientific | 2016 |
| SB Eco Ltd | Construction | 2025 |
| SB Nutrition and Performance Ltd | Arts & recreation | 2020 |
| Scarlet Building Surveys Ltd | Other services | 2023 |
| Scarlet Software Consultancy Ltd | Information & communication | 2022 |
| Scarlets Regional Limited | Arts & recreation | 1997 |
| Scent & Bliss Ltd | Wholesale & retail | 2025 |
| Science Channel Limited | Information & communication | 1997 |
| SCIENCE3 Ltd | Arts & recreation | 2013 |
| Scott Living Ltd | Administrative & support | 2016 |
| SCS Cleaning Limited | Administrative & support | 2021 |
| SCS Development Ltd | Real estate | 2021 |
| SCS Laundry Service Limited | Other services | 2022 |
| SCS Renovations Limited | Construction | 2022 |
| SCS Sewerynek Holding Ltd | Financial services | 2022 |
| SD Property Rentals Ltd | Real estate | 2025 |
| SE Boiler Solutions Ltd | Construction | 2022 |
| Sea at the Marina Ltd | Education | 2022 |
| Seaside Garage Ltd | Wholesale & retail | 2015 |
| Seaside Sports & Social Club Ltd | Arts & recreation | 2012 |
| Seaside Valeting Limited | Wholesale & retail | 2022 |
| Securicall U.K. Limited | Other services | 1994 |
| Security Direct Systems Ltd | Administrative & support | 2020 |
| Security Services KWO Ltd | Administrative & support | 2022 |
| Sedge Maritime Services Ltd | Transport & logistics | 2012 |
| SEE and SEW CIC | Manufacturing | 2025 |
| Sendentity Ltd | Health & social care | 2025 |
| Seneca Property Group Ltd | Construction | 2023 |
| Seren Newydd Properties Ltd | Real estate | 2026 |
| Serendipity Childcare Ltd | Health & social care | 2025 |
| Service Ready Limited | Information & communication | 2024 |
| SET in Motion Ltd | Information & communication | 2020 |
| SFC2026 Limited | Hospitality | 2026 |
| Sgd-Pcb Design Ltd | Professional & scientific | 2023 |
| Shali Trading Ltd | Wholesale & retail | 2025 |
| Shapewright Services Limited | Administrative & support | 2007 |
| Shapton Limited | Professional & scientific | 2014 |
| Shareen Geers Event Management Ltd | Real estate | 2018 |
| Shareen Geers Limited | Real estate | 2023 |
| Sharon and Dexter Property Ltd | Households | 2025 |
| Shaun Anthony Jones Limited | Transport & logistics | 2021 |
| Sheldon Bathrooms Ltd | Construction | 2025 |
| Shire Coffee Company Ltd | Manufacturing | 2019 |
| Shire Coffee Events Ltd | Manufacturing | 2023 |
| Shivarov 2020 Ltd | Transport & logistics | 2020 |
| Short Bros Homes (2) Limited | Construction | 2020 |
| Short Bros Homes (Kidwelly) Limited | Construction | 2020 |
| Short Bros Homes (Pontlliw) Limited | Construction | 2020 |
| Short Bros Homes Limited | Energy | 2015 |
| Short Property Lettings Ltd | Real estate | 2021 |
| Shufflebottom Partners LLP | | 2024 |
| Sian Davies Coaching Ltd | Education | 2025 |
| SIC Properties Ltd | Real estate | 2025 |
| Siddell Environmental Services Limited | Water & waste | 2002 |
| Signature Camper Vans Ltd | Manufacturing | 2019 |
| Signature Campervan Production Ltd | Manufacturing | 2019 |
| Signature Campervan Sales Ltd | Wholesale & retail | 2019 |
| Silani Solutions Limited | Information & communication | 2026 |
| Silcox Family Limited | Other services | 2016 |
| Silver Oak Homes & Assets Ltd | Real estate | 2025 |
| Silver Oak Property Limited | Real estate | 2019 |
| Sion Dafydd Williams Sports Massage Therapist Limited | Education | 2026 |