| Siddington Hall Management Company Limited | Households | 2006 |
| Sidekick Business Development Ltd | Professional & scientific | 2020 |
| Sidekick Holdings Ltd | Financial services | 2026 |
| Sidekick Venture Studio Ltd | Information & communication | 2025 |
| Sideway Subs Ltd | Hospitality | 2019 |
| Siena Consulting Ltd | Professional & scientific | 2026 |
| Sigebyte Ltd | Information & communication | 2026 |
| Sightful Ltd | Information & communication | 2026 |
| Signal & Benchmark Ltd | Professional & scientific | 2026 |
| Signal Origin Ltd | Professional & scientific | 2025 |
| Signature Escapes Ltd | Real estate | 2024 |
| Signature Investments Cornwall Ltd | Real estate | 2026 |
| Signature Stays Management Ltd | Hospitality | 2024 |
| Signcraft Limited | Manufacturing | 2001 |
| Siksa Ltd | Hospitality | 2019 |
| Sila Dining Limited | Hospitality | 2026 |
| Sileby Green Management Company Limited | Households | 2025 |
| Silicon Sky Limited | Information & communication | 2019 |
| Silicon Wireless Limited | Financial services | 2019 |
| Silicone Moulds Ltd | Manufacturing | 2024 |
| Silk Mill Court of Winchcombe Limited | Households | 1978 |
| Silk Wallah Limited | Wholesale & retail | 2012 |
| Silva Psychological Services Ltd | Professional & scientific | 2021 |
| Silver Agency Limited | Professional & scientific | 2005 |
| Silver Global Care Limited | Health & social care | 2025 |
| Silver Moon Cheltenham Limited | Wholesale & retail | 2006 |
| Silver Stoat Services Limited | Professional & scientific | 2020 |
| Silver Tree Services (STS) Limited | Extraterritorial | 2023 |
| Silver Tree Wealth Management Limited | Financial services | 2013 |
| Silverblue Homes Ltd. | Construction | 2014 |
| Silverfox Records Ltd | Wholesale & retail | 2018 |
| Silverjade Limited | Real estate | 2025 |
| Silversnug Limited | Administrative & support | 2021 |
| Silvertwist Limited | Information & communication | 1992 |
| SIM Cube Ltd | Information & communication | 2020 |
| Simazi Limited | Real estate | 2024 |
| Simia Forestry Ltd | Agriculture & fishing | 2018 |
| Simms Limited | Construction | 2007 |
| Simon Brooks Education Ltd | Education | 2018 |
| Simon Burn Solicitors Limited | Professional & scientific | 2008 |
| Simon Holland Consulting Limited | Professional & scientific | 2025 |
| Simon Mchugh Limited | Construction | 2017 |
| Simon Milling & Baking Limited | Manufacturing | 2014 |
| Simon Tobias Heating and Plumbing Ltd | Construction | 2015 |
| Simpkin Limited | Administrative & support | 2000 |
| Simplex Building Limited | Construction | 2013 |
| Simplex Mobile Ltd. | Information & communication | 2014 |
| Simplify Consultancy Ltd | Professional & scientific | 2022 |
| Simplii Finance Ltd | Financial services | 2023 |
| Simplii Invest Ltd | Real estate | 2021 |
| Simplii Media Ltd | Professional & scientific | 2023 |
| Simplii Property Ltd | Real estate | 2021 |
| Simplii Success Ltd | Education | 2022 |
| Simply Align Limited | Education | 2025 |
| Simply Canada Ltd | Wholesale & retail | 2021 |
| Simply Cleaning Ltd | Administrative & support | 2019 |
| Simply Fitted Limited | Construction | 2006 |
| Simply Partnerships Ltd | Information & communication | 2018 |
| Simplychiro Limited | Health & social care | 2014 |
| Simpson's of Cheltenham Limited | Hospitality | 2009 |
| Simpsons in Stroud Limited | Hospitality | 2017 |
| Simrom Investments Limited | Professional & scientific | 2015 |
| Sims Consultancy Brewood Limited | Education | 2017 |
| Sinai Journeys Limited | Administrative & support | 2011 |
| Sinbad Ltd | Professional & scientific | 2003 |
| Sincere Traders Ltd | Wholesale & retail | 2024 |
| Sinclair Family Investments Ltd | Financial services | 2026 |
| Sinclairmoss Ltd | Construction | 2025 |
| Singell Properties Ltd | Real estate | 2019 |
| Singh Thiara Ltd | Information & communication | 2014 |
| Singlestore UK, Ltd | Information & communication | 2019 |
| Singularity Shift Ltd | Professional & scientific | 2025 |
| Sinton Court Management Ltd | Real estate | 2016 |
| Sips Consultancy Ltd | Professional & scientific | 2024 |
| SIR Plumbalot Ltd | Construction | 2022 |
| Sister Sister Collective Ltd | Wholesale & retail | 2019 |
| Sisu Pancakes Franchise Ltd | Wholesale & retail | 2024 |
| Sisu Pancakes Ltd | Wholesale & retail | 2021 |
| SIT and Stay Properties Ltd | Hospitality | 2025 |
| Sita Holdings Limited | Real estate | 2021 |
| Sitch Properties Limited | Real estate | 2025 |
| Siteweld UK Ltd | Professional & scientific | 2011 |
| Sitr Midlands Associates Ltd | Water & waste | 2009 |
| SIX Commercial Limited | Construction | 2020 |
| SIX Different Ways Ltd | Information & communication | 2025 |
| SIX Waves Digital Limited | Professional & scientific | 2023 |
| Sixteen Gallery Ltd | Wholesale & retail | 2021 |
| Sixways Wine Bar Ltd | Hospitality | 2020 |
| SJ Dear Group Limited | Other services | 2022 |
| SJ Dear Productions Limited | Information & communication | 2023 |
| SJ Griffiths Coaching Ltd | Education | 2019 |
| SJ Naumowicz Consulting Ltd | Professional & scientific | 2015 |
| SJ Psychology Ltd | Health & social care | 2022 |
| SJ Signature Developments Ltd | Construction | 2024 |
| SJ Tansey Consultancy Ltd | Information & communication | 2016 |
| SJ Walker Properties Limited | Real estate | 2023 |
| SJB Project Management Limited | Professional & scientific | 2007 |
| SJC Building and Maintenance Ltd | Construction | 2023 |
| SJC Lettings and Property Management Ltd | Real estate | 2025 |
| SJD Creatives Limited | Professional & scientific | 2023 |