| Swiftsenduk Ltd | Transport & logistics | 2024 |
| Swim at 55 Limited | Arts & recreation | 2022 |
| Swimlife UK Ltd. | Construction | 1998 |
| Swimtime RW Limited | Arts & recreation | 2010 |
| Swinton Excavations Ltd | Administrative & support | 2021 |
| Swinton Park Golf and Country Club 2017 Limited | Real estate | 2017 |
| Swish & Shine Cleaning Services Ltd | Administrative & support | 2026 |
| Swish Commercial Cleaning Ltd | Administrative & support | 2020 |
| Swish Housekeeping Limited | Administrative & support | 2012 |
| Swish Housekeeping Residential Ltd | Administrative & support | 2021 |
| Swisspearl GB Ltd | Wholesale & retail | 1985 |
| Switch Electricians Ltd | Construction | 2024 |
| Switch Fitness Limited | Arts & recreation | 2008 |
| Switch Roles Limited | Administrative & support | 2023 |
| Switch WMS Consulting Ltd | Professional & scientific | 2021 |
| Switching Cars Ltd | Wholesale & retail | 2018 |
| Swivel Studios Ltd | Wholesale & retail | 2024 |
| SWQ Engineering Limited | Professional & scientific | 2017 |
| Swym Ltd | Other services | 2024 |
| SY Creative Ltd | Administrative & support | 2026 |
| SYA Barber Warrington Ltd | Other services | 2026 |
| Sycamore Cottage Property Limited | Real estate | 2025 |
| Sycamore Fisheries Limited | Agriculture & fishing | 2007 |
| Sycamore Homes (NW) Ltd | Construction | 2015 |
| Sycamore Send Support Services Ltd | Education | 2023 |
| Syddal Consulting Ltd | Professional & scientific | 2021 |
| Sydney Reeve Limited | Administrative & support | 2017 |
| Syed Engineering Limited | Administrative & support | 2014 |
| Syjay Limited | Wholesale & retail | 2010 |
| Sykes Manufacturing Limited | Professional & scientific | 2002 |
| Sykes Seafood Holdings Limited | Wholesale & retail | 1998 |
| Sykes Seafood Investments Limited | Wholesale & retail | 2025 |
| Sykes Seafood Limited | Wholesale & retail | 1988 |
| Sykes Seafood Property Limited | Real estate | 2025 |
| Sylwia Ziminska Social Work Ltd | Health & social care | 2024 |
| Symmetry LAB Aesthetics Ltd | Other services | 2024 |
| Symons Inns Limited | Hospitality | 1997 |
| Symun Limited | Wholesale & retail | 2012 |
| Synago Ltd | Information & communication | 2011 |
| Syncovision Limited | Administrative & support | 2013 |
| Syndetic Limited | Information & communication | 2006 |
| Synergi AIM Ltd | Administrative & support | 2024 |
| Synergie Engineering Limited | Professional & scientific | 2016 |
| Synergistica Limited | Professional & scientific | 2025 |
| Synergy AJH Limited | Other services | 2021 |
| Synergy Bridge Ltd | Information & communication | 2025 |
| Synergy Consultancy Management Ltd | Professional & scientific | 2022 |
| Synergy Digital Health Innovation Ltd | Administrative & support | 2022 |
| Synergy Electric Solutions Ltd | Construction | 2018 |
| Synergy Group M&E Ltd | Construction | 2025 |
| Synergy Group Services NW Limited | Construction | 2025 |
| Synergy Investment Management Ltd | Financial services | 2015 |
| Synergy Property Investments LLP | | 2015 |
| Synergy Supply Planning Limited | Public administration | 2021 |
| Synergy Transmission & Distribution Solutions Limited | Administrative & support | 2014 |
| Synergyplus Consulting Limited | Professional & scientific | 2014 |
| Synextra Limited | Information & communication | 2014 |
| Synterra Consulting Limited | Administrative & support | 2025 |
| Syntro Services Limited | Administrative & support | 2025 |
| Synyega Holdings Limited | Information & communication | 2018 |
| Synyega Limited | Administrative & support | 2015 |
| Syrah Patel Developments Limited | Real estate | 2021 |
| Syrenis Limited | Information & communication | 2000 |
| SYS ENG Consulting Ltd | Professional & scientific | 2012 |
| Sysprep DRP Limited | Information & communication | 2015 |
| Systaer Consulting Limited | Administrative & support | 2009 |
| Systech Engineers Limited | Administrative & support | 2013 |
| System 2 Analytics Ltd | Information & communication | 2024 |
| System Completion Services Ltd | Professional & scientific | 2024 |
| System CX Ltd | Administrative & support | 2024 |
| System Health Limited | Professional & scientific | 2022 |
| System Trader Limited | Information & communication | 2008 |
| Systems & Instrumentation Solutions Limited | Administrative & support | 2012 |
| Systems Concepts and Solutions Ltd | Professional & scientific | 2022 |
| Systems Integration Services Limited | Professional & scientific | 2018 |
| Systima Group Ltd | Professional & scientific | 2026 |
| SZ Locum Limited | Administrative & support | 2015 |
| SZB Consulting Ltd | Professional & scientific | 2025 |
| Szel Limited | Other services | 2019 |
| Szulc IT Consulting Limited | Information & communication | 2018 |
| Sørensen & Stein Consulting Limited | Professional & scientific | 2015 |
| T & S NOY Limited | Financial services | 2022 |
| T & T Heaven Ltd | Wholesale & retail | 2022 |
| T & T Process Engineering Limited | Administrative & support | 2008 |
| T and S NOY Family Limited | Financial services | 2022 |
| T D S Training & Development Solutions Ltd | Education | 2006 |
| T Godfree Consultancy Ltd | Professional & scientific | 2014 |
| T H Jackson Services Ltd | Professional & scientific | 2022 |
| T Harding Property Limited | Real estate | 2018 |
| T J Birmingham Limited | Administrative & support | 2023 |
| T J Hopkins Ltd | Construction | 2013 |
| T J Marshall Consultancy Limited | Professional & scientific | 2016 |
| T J Taylor Consultancy Services Ltd | Information & communication | 2017 |
| T Jakir Limited | Real estate | 2025 |
| T L S Data Limited | Information & communication | 2003 |
| T Lethbridge Limited | Extraterritorial | 1972 |
| T Little QA Testing Ltd | Professional & scientific | 2018 |
| T O’Keefe Contracting Ltd | Administrative & support | 2026 |
| T P S Plant & Groundwork Limited | Construction | 2004 |
| T Shawcross Limited | Administrative & support | 2015 |