| Sycom Delta Ltd | Information & communication | 2012 |
| Sydfredt Properties Ltd | Real estate | 2025 |
| Syed Aamir ALI Ltd | Information & communication | 2017 |
| Syed Mubashar ALI Ltd | Transport & logistics | 2022 |
| SYH Solutions Ltd | Information & communication | 2024 |
| SYL Project Solution Ltd | Construction | 2012 |
| Sylhet Construction Services Limited | Construction | 2025 |
| Sylvia K Ltd | Other services | 2012 |
| Sym-Mk Ltd | Real estate | 2012 |
| Symbia Solutions Ltd | Professional & scientific | 2010 |
| Symbiote Ltd | Wholesale & retail | 2025 |
| Symphony APS Ltd | Information & communication | 2012 |
| Symphony Professional Solutions Ltd | Information & communication | 2013 |
| SYMPHONY365 Limited | Professional & scientific | 2012 |
| SYN WIN Properties Ltd | Real estate | 2022 |
| SYN X Fuels UK Limited | Professional & scientific | 2022 |
| SYN3RGY Capital Limited | Financial services | 2022 |
| Synapse Global Limited | Professional & scientific | 2014 |
| Synchronoss Technologies Data Centre Limited | Information & communication | 1999 |
| Syncopate Limited | Professional & scientific | 2005 |
| Syncrocell Ltd | Manufacturing | 2025 |
| Syncronate Ltd | Professional & scientific | 2021 |
| Syndica Publishing Ltd | Information & communication | 2024 |
| Synergex Ltd | Wholesale & retail | 2026 |
| Synergi Recruitment Ltd | Administrative & support | 2025 |
| Synergie HR Ltd | Administrative & support | 2026 |
| Synergipoint Ltd | Real estate | 2025 |
| Synergistic Resources Limited | Information & communication | 2011 |
| Synergy Alliance Limited | Administrative & support | 2007 |
| Synergy Estate Management Ltd | Real estate | 2026 |
| Synergy Legal Ltd | Education | 2017 |
| Synergy Property Staging Ltd | Wholesale & retail | 2025 |
| Synergy Sky Limited | Information & communication | 2018 |
| Synergypoint Consulting Limited | Information & communication | 2024 |
| Synology UK Limited | Wholesale & retail | 2008 |
| Synteric Limited | Information & communication | 2025 |
| Synthinx Ltd | Information & communication | 2024 |
| Synventive Acquisition UK Limited | Professional & scientific | 2005 |
| Synventive Acquisition Unlimited | Manufacturing | 2005 |
| Synventive Holding Limited | Manufacturing | 2003 |
| Synventive Molding Solutions Limited | Manufacturing | 1993 |
| SYS IQ Ltd | Information & communication | 2013 |
| Sys-Stem Ltd | Professional & scientific | 2025 |
| Sysline Ltd | Information & communication | 2015 |
| Sysmex UK Limited | Health & social care | 1991 |
| Systech Management & Solutions Ltd | Other services | 2020 |
| Systech Solutions Limited | Other services | 2012 |
| System Compliance Solutions Limited | Administrative & support | 2018 |
| Systemkind Ltd | Information & communication | 2019 |
| Systena Limited | Information & communication | 2004 |
| Systime Group Limited | Information & communication | 2013 |
| Systime Limited | Information & communication | 2022 |
| Syzygy Leisure Limited | Arts & recreation | 2003 |
| Szimistyle Ltd | Transport & logistics | 2023 |
| Szyszka Ltd | Transport & logistics | 2014 |
| T & I Kebab Limited | Hospitality | 2025 |
| T & B Mechanical Services Limited | | 1986 |
| T & C Recycling Limited | Water & waste | 2021 |
| T & K Leisure Limited | Arts & recreation | 2006 |
| T & L Flooring Limited | Construction | 2008 |
| T & T Plumbers Ltd | Construction | 2026 |
| T Allen Developments Ltd | Other services | 2014 |
| T and N Consulting Limited | Information & communication | 2006 |
| T ASH Property Ltd | Administrative & support | 2017 |
| T B Hurley Holdings Limited | Financial services | 2018 |
| T B I Media Employee Ownership Trust Limited | Administrative & support | 2024 |
| T B I Media Limited | Information & communication | 2007 |
| T B Tech MK Limited | Wholesale & retail | 2017 |
| T BAH Trading Limited | Wholesale & retail | 2021 |
| T E Plumbing Limited | Construction | 2012 |
| T F S Loans Limited | Financial services | 2008 |
| T Fricker Ltd | Construction | 2019 |
| T G Autos Limited | Wholesale & retail | 2012 |
| T J Rose Landscapes Ltd | Administrative & support | 2026 |
| T MAY Consultants Limited | Professional & scientific | 2006 |
| T O'Donoghue Limited | Manufacturing | 1959 |
| T R Healthcare Limited | Health & social care | 2017 |
| T W Automotive Ltd | Wholesale & retail | 2019 |
| T&A Install Ltd | Construction | 2019 |
| T&I Builders MK Ltd | Construction | 2023 |
| T&L Ashmead Ltd | Hospitality | 2024 |
| T&L Property Holdings Limited | Real estate | 2021 |
| T&M Alliance LLP | | 2021 |
| T&M Food Europe Ltd | Hospitality | 2026 |
| T&M Global Trading UK Ltd | Wholesale & retail | 2026 |
| T&N Couriers Private Limited | Transport & logistics | 2010 |
| T&R Pubs Ltd | Hospitality | 2025 |
| T&R Sons Ltd | Real estate | 2021 |
| T&T BUI Limited | Other services | 2024 |
| T&T Global Group Ltd | Education | 2025 |
| T&T Social Work Solutions Ltd | Health & social care | 2015 |
| T-H-E Events Ltd | Education | 2024 |
| T-Mobile Holdings Limited | Professional & scientific | 1999 |
| T-Systems Limited | Information & communication | 1982 |
| T.A. Boxall & Company Limited | Construction | 1980 |
| T.A.D Global Construction Ltd | Construction | 2020 |
| T.Cross & Sons(Hartwell)Limited | Agriculture & fishing | 1961 |
| T.D. PUB Management Limited | Hospitality | 2020 |
| T.E.Hopper Limited | Construction | 2009 |
| T.H. Works Limited | Manufacturing | 2023 |