| Surf the Shop Ltd. | Wholesale & retail | 2016 |
| Surge Electrical Ltd | Construction | 2019 |
| Surple Energy Limited | Information & communication | 2018 |
| Survey My House Ltd | Construction | 2022 |
| Surya Holdings Ltd | Financial services | 2023 |
| Sushil (Risca) Ltd | Hospitality | 2015 |
| Susie Lawrence Consulting Ltd | Administrative & support | 2007 |
| Sussex View Management Company Limited | Households | 2007 |
| Sustainability Changemakers Limited | Professional & scientific | 2023 |
| Sustainability Sphere CIC | Education | 2025 |
| Sustainable Heat Solutions Ltd | Construction | 2022 |
| Sustainable Studio Architects Ltd | Professional & scientific | 2019 |
| Sustainable Survey Limited | Professional & scientific | 2023 |
| Sutherland Arms Ltd | Hospitality | 2022 |
| Sutherland Croft Blinds Ltd | Wholesale & retail | 2022 |
| Sutton Barns Management Company (2) Limited | Households | 2004 |
| SV Hospitality Ltd | Hospitality | 2025 |
| SV300 Wealth & Estates Group Ltd | Real estate | 2020 |
| SV9 Promotions Ltd | Arts & recreation | 2024 |
| Svrm Media Ltd | Professional & scientific | 2024 |
| SW Consultancy Practice Ltd | Professional & scientific | 2018 |
| SW Home Healthcare Ltd | Health & social care | 2024 |
| SW Tent Pegging Assoc Ltd | Arts & recreation | 2026 |
| SW Vape Supplies Ltd | Wholesale & retail | 2020 |
| SW Vehicle Body Repair Ltd | Wholesale & retail | 2024 |
| SW Wellbeing Alliance CIC | Health & social care | 2022 |
| Swains Field Limited | Agriculture & fishing | 1967 |
| Swan at Forton Ltd | Hospitality | 2026 |
| Swann Counselling and Therapy Services Ltd | Health & social care | 2026 |
| Swansea City Cleaning Ltd | Administrative & support | 2026 |
| Swansea Property Holdings Ltd | Real estate | 2024 |
| SWC4 Limited | Professional & scientific | 2003 |
| Sweet Dessert Cardiff Ltd | Wholesale & retail | 2019 |
| Sweet Learn Ltd | Information & communication | 2018 |
| Sweetland Associates Limited | Financial services | 2003 |
| Sweets & Scents Ltd | Wholesale & retail | 2025 |
| Sweetsdelight Ltd | Wholesale & retail | 2025 |
| Sweetwater Developments Ltd | Real estate | 2025 |
| Swift Cleaning Services Commercial Ltd | Administrative & support | 2024 |
| Swift Fibre Ltd | Information & communication | 2021 |
| Swift Kitchen Doors Ltd | Construction | 2025 |
| Swift Lifting Ltd | Construction | 2024 |
| Swift Serve Logistics Ltd | Transport & logistics | 2025 |
| Swift Signs Ltd | Other services | 2019 |
| Swift Steel Services Limited | Manufacturing | 1990 |
| Swift Upvc West Ltd | Construction | 2025 |
| Swiftchannel Services Limited | Transport & logistics | 2026 |
| Swinnerton Contractors Limited | Professional & scientific | 2012 |
| Swinnertons Ltd | Real estate | 2024 |
| Swirl Ltd | Real estate | 2022 |
| SWM Fabrication Ltd | Administrative & support | 2016 |
| Swmae Holdings Limited | Financial services | 2024 |
| SWN Y Nant Limited | Households | 2020 |
| Swop IT Limited | Manufacturing | 2024 |
| Swsmedics Limited | Health & social care | 2017 |
| SWW Consultancy Limited | Professional & scientific | 2016 |
| Swyd Ltd | Other services | 2013 |
| Sydney’S Bath Ltd | Hospitality | 2018 |
| SYK Property Ltd | Other services | 2024 |
| Sykes Brothers Limited | Real estate | 2025 |
| Sylhet Dine Limited | Hospitality | 2026 |
| SYLHET6142 Ltd | Hospitality | 2024 |
| Syml Admin Limited | Administrative & support | 2017 |
| Symphony Education Limited | Education | 2024 |
| Symphony Kingdom UK Ltd | Professional & scientific | 2025 |
| Sync Travel & Money Transfer Ltd | Administrative & support | 2025 |
| Syndicate Terrace 1964 Limited | Extraterritorial | 2014 |
| Syner-Chi Wellbeing Limited | Other services | 2019 |
| Synergy Lighting Ltd | Manufacturing | 2002 |
| Synergy Plastics Limited | Manufacturing | 1995 |
| Syniad LLP | | 2014 |
| SYNKT21.8 Limited | Professional & scientific | 2024 |
| Synone Property Management Limited | Real estate | 2011 |
| Synthesis Wales Therapies Limited | Health & social care | 2021 |
| Syrus Energy Cardigan Limited | Energy | 2013 |
| Syrus Energy Cowbridge Limited | Energy | 2013 |
| Syrus Energy Limited | Professional & scientific | 2002 |
| Syrus Limited | Administrative & support | 2011 |
| System Cell Ltd | Manufacturing | 2002 |
| Systemise Engineering Ltd | Professional & scientific | 2019 |
| Systems Analysis Design and Support Limited | Information & communication | 1988 |
| Systemspace Limited | Real estate | 2000 |
| Szot Construction Ltd | Construction | 2019 |
| Szot Rendering Ltd | Construction | 2022 |
| T & B Investment Properties Ltd | Households | 2021 |
| T a Tran Nails Ltd | Other services | 2022 |
| T and a Holdco Limited | Real estate | 2023 |
| T and a Property Management LLP | | 2020 |
| T and T Filtration Limited | Manufacturing | 2007 |
| T E Newport Development Ltd | Real estate | 2019 |
| T J Vaughan & Co Limited | Agriculture & fishing | 2022 |
| T J Hunt Ltd | Manufacturing | 2003 |
| T J Morris Plant Hire Ltd | Construction | 2005 |
| T S Hunt Carpentry & Joinery Limited | Construction | 2002 |
| T Sarwar Contractor Solutions Ltd | Financial services | 2011 |
| T Virgo Upvc & Building Ltd | Construction | 2020 |
| T&A Construction Group Limited | Construction | 2019 |
| T&T Digital Limited | Information & communication | 2021 |
| T&T Flooring Limited | Construction | 2024 |
| T&V Services Limited | Professional & scientific | 2021 |