| South Wales Printing Company Limited | Manufacturing | 2025 |
| South Wales Property Developments Ltd | Real estate | 2020 |
| South Wales Property Management Ltd | Households | 2024 |
| South Wales Property Sourcing Ltd | Real estate | 2021 |
| South Wales Resurfacing and Groundworks Limited | Construction | 2020 |
| South Wales Stone Ltd | Manufacturing | 2024 |
| South Wales Vehicle Security Ltd | Wholesale & retail | 2022 |
| South Wales Web Solutions Ltd | Information & communication | 2011 |
| South Wales Window Blind Centre Limited | Manufacturing | 1988 |
| South Wales Woodwind Ltd. | Manufacturing | 2010 |
| South West (SW) Contractors Ltd | Construction | 2019 |
| South West Injector Removal Service Ltd | Wholesale & retail | 2024 |
| Southall Avenue Limited | Real estate | 2024 |
| Southampton Sea Charters Limited | Transport & logistics | 2024 |
| Southend Heights Management Company Limited | Households | 2025 |
| Southern County Care Homes Limited | Health & social care | 2025 |
| Southern Skies Paragliding Ltd | Arts & recreation | 2014 |
| Southpaw Properties Limited | Real estate | 2023 |
| Southw Rope Access Ltd | Administrative & support | 2024 |
| Southwood Lewis Ltd | Information & communication | 2017 |
| Sovereign 308 Limited | Other services | 2018 |
| Sovereign Slate Roofing Limited | Wholesale & retail | 2019 |
| Sowden Agri Limited | Construction | 2024 |
| SP Apartments Ltd | Real estate | 2026 |
| SP Bookkeeping Ltd | Professional & scientific | 2026 |
| SP Developments Limited | Real estate | 1994 |
| SP Plant Hire and Sales Ltd | Extraterritorial | 2016 |
| SP Property Leases Ltd | Real estate | 2023 |
| SP Ssas Investments Limited | Real estate | 2022 |
| Space Cadets Records Ltd | Information & communication | 2025 |
| Space SA3 Ltd | Professional & scientific | 2024 |
| Space-Works Construction Ltd | Professional & scientific | 2023 |
| Spaceway Ltd. | Real estate | 1998 |
| Spar West Cross Ltd | Wholesale & retail | 2002 |
| Spark Structures Ltd | Construction | 2021 |
| Sparkle Cleaning LAB Ltd | Administrative & support | 2023 |
| Sparkles of Joy Entertainment Ltd | Administrative & support | 2025 |
| Sparkling Cars Ltd | Wholesale & retail | 2020 |
| Sparkling Launderette Ltd | Other services | 2020 |
| Sparkling Waters Care Limited | Administrative & support | 2018 |
| Sparkling Windows Swansea Ltd | Administrative & support | 2024 |
| Sparkz Electric Ltd | Construction | 2024 |
| Spartan Scaffolding Holdings Limited | Financial services | 2023 |
| Spartan Scaffolding Solutions Limited | Construction | 2013 |
| Spatz Limited | Hospitality | 2003 |
| SPB Motors Ltd | Wholesale & retail | 2025 |
| SPC 2017 Property Limited | Real estate | 2017 |
| Spec Electrical and Ventilation Ltd | Construction | 2018 |
| Special Missions Ltd | Professional & scientific | 2024 |
| Specialised Steel Fabrication Limited | Manufacturing | 2022 |
| Specialist Sprinkler and Plumbing Services Limited | Construction | 2019 |
| Specs Spectrum C.I.C. | Health & social care | 2024 |
| Specta Properties (Swansea) Limited | Real estate | 2024 |
| Spectra Nova PR Ltd | Information & communication | 2025 |
| Spectral Ecology Limited | Professional & scientific | 2025 |
| Spectral Engineering Limited | Professional & scientific | 2024 |
| Spectrum Glass Solutions Ltd. | Manufacturing | 2000 |
| Spectrum Healthcare Agency Limited | Health & social care | 2019 |
| Spectrum Healthcare Powys Limited | Health & social care | 2022 |
| Spectrum Supply Limited | Manufacturing | 2010 |
| Speedshift UK Limited | Other services | 2015 |
| Speedstore Ltd | Other services | 2015 |
| Speedy Cables (London) Limited | Manufacturing | 1975 |
| Spellbinding Ltd | Wholesale & retail | 2025 |
| Spencer Morgan Limited | Wholesale & retail | 2008 |
| Spendwise Limited | Professional & scientific | 2005 |
| SPG Carpentry Ltd | Construction | 2019 |
| SPG Martial Arts Ltd | Arts & recreation | 2025 |
| Sphaera Limited | Information & communication | 2000 |
| Spice Village Yorkshire Limited | Hospitality | 2019 |
| Spice West Cross Ltd | Hospitality | 2019 |
| Spider Music Limited | Education | 2001 |
| Spider's Music School Limited | Education | 2020 |
| Spiiceway Ltd | Hospitality | 2025 |
| Spikesurface Limited | Households | 1986 |
| Spiky Rich Ltd | Wholesale & retail | 2020 |
| Spirit and Soul Limited | Other services | 2025 |
| Spirit Path Limited | Professional & scientific | 2017 |
| Spitalfields Historic Buildings (Sheerness) Limited | Real estate | 2011 |
| SPK Property Solutions Ltd | Construction | 2019 |
| Splatch C.I.C. | Arts & recreation | 2022 |
| SPM Assets Ltd | Construction | 2025 |
| SPO Investments Ltd | Professional & scientific | 2012 |
| Spoke Wraps Limited | Manufacturing | 2015 |
| Sport Passport Limited | Arts & recreation | 2014 |
| Sport Tech UK Limited | Administrative & support | 2009 |
| Sports and Well Being Analytics Limited | Administrative & support | 2016 |
| Sports Perform Limited | Arts & recreation | 2025 |
| Sports Performance Services Limited | Education | 1992 |
| Sports UN Limited | Extraterritorial | 2023 |
| Sportsmed Provisions Ltd | Health & social care | 2024 |
| Spotless Living Limited | Administrative & support | 2015 |
| Spray Solutions Swansea Limited | Construction | 2020 |
| Spring Meadow Care Ltd | Health & social care | 2025 |
| Spring Meadows (Care) Limited | Health & social care | 2005 |
| Springfield Management Company (Horton) Limited | Extraterritorial | 1990 |
| Sprinkler Protect Ltd | Professional & scientific | 2025 |
| Spritemast Limited | Construction | 1998 |
| SPS Premium Properties Ltd | Real estate | 2024 |
| Spurlock Limited | Education | 2018 |